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![Linus Torvalds](/assets/img/avatar_default.png)
Commit 054aa8d439
("fget: check that the fd still exists after getting
a ref to it") fixed a race with getting a reference to a file just as it
was being closed. It was a fairly minimal patch, and I didn't think
re-checking the file pointer lookup would be a measurable overhead,
since it was all right there and cached.
But I was wrong, as pointed out by the kernel test robot.
The 'poll2' case of the will-it-scale.per_thread_ops benchmark regressed
quite noticeably. Admittedly it seems to be a very artificial test:
doing "poll()" system calls on regular files in a very tight loop in
multiple threads.
That means that basically all the time is spent just looking up file
descriptors without ever doing anything useful with them (not that doing
'poll()' on a regular file is useful to begin with). And as a result it
shows the extra "re-check fd" cost as a sore thumb.
Happily, the regression is fixable by just writing the code to loook up
the fd to be better and clearer. There's still a cost to verify the
file pointer, but now it's basically in the noise even for that
benchmark that does nothing else - and the code is more understandable
and has better comments too.
[ Side note: this patch is also a classic case of one that looks very
messy with the default greedy Myers diff - it's much more legible with
either the patience of histogram diff algorithm ]
Link: https://lore.kernel.org/lkml/20211210053743.GA36420@xsang-OptiPlex-9020/
Link: https://lore.kernel.org/lkml/20211213083154.GA20853@linux.intel.com/
Reported-by: kernel test robot <oliver.sang@intel.com>
Tested-by: Carel Si <beibei.si@intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1307 lines
31 KiB
C
1307 lines
31 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* linux/fs/file.c
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*
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* Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
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*
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* Manage the dynamic fd arrays in the process files_struct.
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*/
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#include <linux/syscalls.h>
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#include <linux/export.h>
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#include <linux/fs.h>
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/sched/signal.h>
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#include <linux/slab.h>
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#include <linux/file.h>
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#include <linux/fdtable.h>
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#include <linux/bitops.h>
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#include <linux/spinlock.h>
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#include <linux/rcupdate.h>
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#include <linux/close_range.h>
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#include <net/sock.h>
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#include "internal.h"
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unsigned int sysctl_nr_open __read_mostly = 1024*1024;
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unsigned int sysctl_nr_open_min = BITS_PER_LONG;
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/* our min() is unusable in constant expressions ;-/ */
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#define __const_min(x, y) ((x) < (y) ? (x) : (y))
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unsigned int sysctl_nr_open_max =
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__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;
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static void __free_fdtable(struct fdtable *fdt)
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{
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kvfree(fdt->fd);
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kvfree(fdt->open_fds);
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kfree(fdt);
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}
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static void free_fdtable_rcu(struct rcu_head *rcu)
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{
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__free_fdtable(container_of(rcu, struct fdtable, rcu));
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}
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#define BITBIT_NR(nr) BITS_TO_LONGS(BITS_TO_LONGS(nr))
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#define BITBIT_SIZE(nr) (BITBIT_NR(nr) * sizeof(long))
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/*
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* Copy 'count' fd bits from the old table to the new table and clear the extra
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* space if any. This does not copy the file pointers. Called with the files
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* spinlock held for write.
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*/
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static void copy_fd_bitmaps(struct fdtable *nfdt, struct fdtable *ofdt,
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unsigned int count)
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{
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unsigned int cpy, set;
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cpy = count / BITS_PER_BYTE;
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set = (nfdt->max_fds - count) / BITS_PER_BYTE;
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memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
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memset((char *)nfdt->open_fds + cpy, 0, set);
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memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
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memset((char *)nfdt->close_on_exec + cpy, 0, set);
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cpy = BITBIT_SIZE(count);
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set = BITBIT_SIZE(nfdt->max_fds) - cpy;
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memcpy(nfdt->full_fds_bits, ofdt->full_fds_bits, cpy);
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memset((char *)nfdt->full_fds_bits + cpy, 0, set);
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}
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/*
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* Copy all file descriptors from the old table to the new, expanded table and
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* clear the extra space. Called with the files spinlock held for write.
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*/
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static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
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{
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size_t cpy, set;
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BUG_ON(nfdt->max_fds < ofdt->max_fds);
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cpy = ofdt->max_fds * sizeof(struct file *);
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set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
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memcpy(nfdt->fd, ofdt->fd, cpy);
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memset((char *)nfdt->fd + cpy, 0, set);
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copy_fd_bitmaps(nfdt, ofdt, ofdt->max_fds);
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}
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static struct fdtable * alloc_fdtable(unsigned int nr)
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{
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struct fdtable *fdt;
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void *data;
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/*
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* Figure out how many fds we actually want to support in this fdtable.
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* Allocation steps are keyed to the size of the fdarray, since it
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* grows far faster than any of the other dynamic data. We try to fit
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* the fdarray into comfortable page-tuned chunks: starting at 1024B
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* and growing in powers of two from there on.
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*/
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nr /= (1024 / sizeof(struct file *));
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nr = roundup_pow_of_two(nr + 1);
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nr *= (1024 / sizeof(struct file *));
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/*
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* Note that this can drive nr *below* what we had passed if sysctl_nr_open
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* had been set lower between the check in expand_files() and here. Deal
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* with that in caller, it's cheaper that way.
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*
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* We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
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* bitmaps handling below becomes unpleasant, to put it mildly...
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*/
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if (unlikely(nr > sysctl_nr_open))
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nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
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fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL_ACCOUNT);
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if (!fdt)
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goto out;
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fdt->max_fds = nr;
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data = kvmalloc_array(nr, sizeof(struct file *), GFP_KERNEL_ACCOUNT);
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if (!data)
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goto out_fdt;
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fdt->fd = data;
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data = kvmalloc(max_t(size_t,
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2 * nr / BITS_PER_BYTE + BITBIT_SIZE(nr), L1_CACHE_BYTES),
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GFP_KERNEL_ACCOUNT);
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if (!data)
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goto out_arr;
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fdt->open_fds = data;
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data += nr / BITS_PER_BYTE;
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fdt->close_on_exec = data;
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data += nr / BITS_PER_BYTE;
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fdt->full_fds_bits = data;
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return fdt;
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out_arr:
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kvfree(fdt->fd);
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out_fdt:
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kfree(fdt);
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out:
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return NULL;
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}
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/*
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* Expand the file descriptor table.
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* This function will allocate a new fdtable and both fd array and fdset, of
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* the given size.
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* Return <0 error code on error; 1 on successful completion.
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* The files->file_lock should be held on entry, and will be held on exit.
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*/
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static int expand_fdtable(struct files_struct *files, unsigned int nr)
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__releases(files->file_lock)
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__acquires(files->file_lock)
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{
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struct fdtable *new_fdt, *cur_fdt;
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spin_unlock(&files->file_lock);
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new_fdt = alloc_fdtable(nr);
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/* make sure all fd_install() have seen resize_in_progress
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* or have finished their rcu_read_lock_sched() section.
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*/
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if (atomic_read(&files->count) > 1)
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synchronize_rcu();
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spin_lock(&files->file_lock);
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if (!new_fdt)
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return -ENOMEM;
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/*
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* extremely unlikely race - sysctl_nr_open decreased between the check in
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* caller and alloc_fdtable(). Cheaper to catch it here...
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*/
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if (unlikely(new_fdt->max_fds <= nr)) {
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__free_fdtable(new_fdt);
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return -EMFILE;
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}
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cur_fdt = files_fdtable(files);
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BUG_ON(nr < cur_fdt->max_fds);
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copy_fdtable(new_fdt, cur_fdt);
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rcu_assign_pointer(files->fdt, new_fdt);
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if (cur_fdt != &files->fdtab)
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call_rcu(&cur_fdt->rcu, free_fdtable_rcu);
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/* coupled with smp_rmb() in fd_install() */
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smp_wmb();
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return 1;
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}
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/*
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* Expand files.
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* This function will expand the file structures, if the requested size exceeds
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* the current capacity and there is room for expansion.
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* Return <0 error code on error; 0 when nothing done; 1 when files were
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* expanded and execution may have blocked.
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* The files->file_lock should be held on entry, and will be held on exit.
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*/
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static int expand_files(struct files_struct *files, unsigned int nr)
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__releases(files->file_lock)
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__acquires(files->file_lock)
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{
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struct fdtable *fdt;
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int expanded = 0;
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repeat:
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fdt = files_fdtable(files);
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/* Do we need to expand? */
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if (nr < fdt->max_fds)
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return expanded;
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/* Can we expand? */
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if (nr >= sysctl_nr_open)
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return -EMFILE;
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if (unlikely(files->resize_in_progress)) {
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spin_unlock(&files->file_lock);
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expanded = 1;
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wait_event(files->resize_wait, !files->resize_in_progress);
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spin_lock(&files->file_lock);
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goto repeat;
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}
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/* All good, so we try */
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files->resize_in_progress = true;
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expanded = expand_fdtable(files, nr);
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files->resize_in_progress = false;
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wake_up_all(&files->resize_wait);
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return expanded;
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}
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static inline void __set_close_on_exec(unsigned int fd, struct fdtable *fdt)
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{
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__set_bit(fd, fdt->close_on_exec);
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}
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static inline void __clear_close_on_exec(unsigned int fd, struct fdtable *fdt)
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{
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if (test_bit(fd, fdt->close_on_exec))
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__clear_bit(fd, fdt->close_on_exec);
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}
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static inline void __set_open_fd(unsigned int fd, struct fdtable *fdt)
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{
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__set_bit(fd, fdt->open_fds);
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fd /= BITS_PER_LONG;
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if (!~fdt->open_fds[fd])
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__set_bit(fd, fdt->full_fds_bits);
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}
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static inline void __clear_open_fd(unsigned int fd, struct fdtable *fdt)
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{
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__clear_bit(fd, fdt->open_fds);
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__clear_bit(fd / BITS_PER_LONG, fdt->full_fds_bits);
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}
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static unsigned int count_open_files(struct fdtable *fdt)
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{
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unsigned int size = fdt->max_fds;
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unsigned int i;
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/* Find the last open fd */
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for (i = size / BITS_PER_LONG; i > 0; ) {
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if (fdt->open_fds[--i])
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break;
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}
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i = (i + 1) * BITS_PER_LONG;
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return i;
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}
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static unsigned int sane_fdtable_size(struct fdtable *fdt, unsigned int max_fds)
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{
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unsigned int count;
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count = count_open_files(fdt);
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if (max_fds < NR_OPEN_DEFAULT)
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max_fds = NR_OPEN_DEFAULT;
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return min(count, max_fds);
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}
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/*
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* Allocate a new files structure and copy contents from the
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* passed in files structure.
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* errorp will be valid only when the returned files_struct is NULL.
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*/
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struct files_struct *dup_fd(struct files_struct *oldf, unsigned int max_fds, int *errorp)
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{
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struct files_struct *newf;
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struct file **old_fds, **new_fds;
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unsigned int open_files, i;
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struct fdtable *old_fdt, *new_fdt;
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*errorp = -ENOMEM;
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newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
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if (!newf)
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goto out;
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atomic_set(&newf->count, 1);
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spin_lock_init(&newf->file_lock);
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newf->resize_in_progress = false;
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init_waitqueue_head(&newf->resize_wait);
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newf->next_fd = 0;
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new_fdt = &newf->fdtab;
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new_fdt->max_fds = NR_OPEN_DEFAULT;
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new_fdt->close_on_exec = newf->close_on_exec_init;
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new_fdt->open_fds = newf->open_fds_init;
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new_fdt->full_fds_bits = newf->full_fds_bits_init;
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new_fdt->fd = &newf->fd_array[0];
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spin_lock(&oldf->file_lock);
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old_fdt = files_fdtable(oldf);
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open_files = sane_fdtable_size(old_fdt, max_fds);
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/*
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* Check whether we need to allocate a larger fd array and fd set.
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*/
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while (unlikely(open_files > new_fdt->max_fds)) {
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spin_unlock(&oldf->file_lock);
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if (new_fdt != &newf->fdtab)
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__free_fdtable(new_fdt);
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new_fdt = alloc_fdtable(open_files - 1);
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if (!new_fdt) {
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*errorp = -ENOMEM;
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goto out_release;
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}
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/* beyond sysctl_nr_open; nothing to do */
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if (unlikely(new_fdt->max_fds < open_files)) {
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__free_fdtable(new_fdt);
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*errorp = -EMFILE;
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goto out_release;
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}
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/*
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* Reacquire the oldf lock and a pointer to its fd table
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* who knows it may have a new bigger fd table. We need
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* the latest pointer.
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*/
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spin_lock(&oldf->file_lock);
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old_fdt = files_fdtable(oldf);
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open_files = sane_fdtable_size(old_fdt, max_fds);
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}
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copy_fd_bitmaps(new_fdt, old_fdt, open_files);
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old_fds = old_fdt->fd;
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new_fds = new_fdt->fd;
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for (i = open_files; i != 0; i--) {
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struct file *f = *old_fds++;
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if (f) {
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get_file(f);
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} else {
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/*
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* The fd may be claimed in the fd bitmap but not yet
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* instantiated in the files array if a sibling thread
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* is partway through open(). So make sure that this
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* fd is available to the new process.
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*/
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__clear_open_fd(open_files - i, new_fdt);
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}
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rcu_assign_pointer(*new_fds++, f);
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}
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spin_unlock(&oldf->file_lock);
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|
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/* clear the remainder */
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memset(new_fds, 0, (new_fdt->max_fds - open_files) * sizeof(struct file *));
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rcu_assign_pointer(newf->fdt, new_fdt);
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return newf;
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|
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out_release:
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kmem_cache_free(files_cachep, newf);
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out:
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return NULL;
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}
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|
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static struct fdtable *close_files(struct files_struct * files)
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{
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/*
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* It is safe to dereference the fd table without RCU or
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* ->file_lock because this is the last reference to the
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* files structure.
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*/
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struct fdtable *fdt = rcu_dereference_raw(files->fdt);
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unsigned int i, j = 0;
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|
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for (;;) {
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unsigned long set;
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i = j * BITS_PER_LONG;
|
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if (i >= fdt->max_fds)
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break;
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set = fdt->open_fds[j++];
|
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while (set) {
|
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if (set & 1) {
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struct file * file = xchg(&fdt->fd[i], NULL);
|
|
if (file) {
|
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filp_close(file, files);
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cond_resched();
|
|
}
|
|
}
|
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i++;
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set >>= 1;
|
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}
|
|
}
|
|
|
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return fdt;
|
|
}
|
|
|
|
void put_files_struct(struct files_struct *files)
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|
{
|
|
if (atomic_dec_and_test(&files->count)) {
|
|
struct fdtable *fdt = close_files(files);
|
|
|
|
/* free the arrays if they are not embedded */
|
|
if (fdt != &files->fdtab)
|
|
__free_fdtable(fdt);
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kmem_cache_free(files_cachep, files);
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|
}
|
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}
|
|
|
|
void exit_files(struct task_struct *tsk)
|
|
{
|
|
struct files_struct * files = tsk->files;
|
|
|
|
if (files) {
|
|
task_lock(tsk);
|
|
tsk->files = NULL;
|
|
task_unlock(tsk);
|
|
put_files_struct(files);
|
|
}
|
|
}
|
|
|
|
struct files_struct init_files = {
|
|
.count = ATOMIC_INIT(1),
|
|
.fdt = &init_files.fdtab,
|
|
.fdtab = {
|
|
.max_fds = NR_OPEN_DEFAULT,
|
|
.fd = &init_files.fd_array[0],
|
|
.close_on_exec = init_files.close_on_exec_init,
|
|
.open_fds = init_files.open_fds_init,
|
|
.full_fds_bits = init_files.full_fds_bits_init,
|
|
},
|
|
.file_lock = __SPIN_LOCK_UNLOCKED(init_files.file_lock),
|
|
.resize_wait = __WAIT_QUEUE_HEAD_INITIALIZER(init_files.resize_wait),
|
|
};
|
|
|
|
static unsigned int find_next_fd(struct fdtable *fdt, unsigned int start)
|
|
{
|
|
unsigned int maxfd = fdt->max_fds;
|
|
unsigned int maxbit = maxfd / BITS_PER_LONG;
|
|
unsigned int bitbit = start / BITS_PER_LONG;
|
|
|
|
bitbit = find_next_zero_bit(fdt->full_fds_bits, maxbit, bitbit) * BITS_PER_LONG;
|
|
if (bitbit > maxfd)
|
|
return maxfd;
|
|
if (bitbit > start)
|
|
start = bitbit;
|
|
return find_next_zero_bit(fdt->open_fds, maxfd, start);
|
|
}
|
|
|
|
/*
|
|
* allocate a file descriptor, mark it busy.
|
|
*/
|
|
static int alloc_fd(unsigned start, unsigned end, unsigned flags)
|
|
{
|
|
struct files_struct *files = current->files;
|
|
unsigned int fd;
|
|
int error;
|
|
struct fdtable *fdt;
|
|
|
|
spin_lock(&files->file_lock);
|
|
repeat:
|
|
fdt = files_fdtable(files);
|
|
fd = start;
|
|
if (fd < files->next_fd)
|
|
fd = files->next_fd;
|
|
|
|
if (fd < fdt->max_fds)
|
|
fd = find_next_fd(fdt, fd);
|
|
|
|
/*
|
|
* N.B. For clone tasks sharing a files structure, this test
|
|
* will limit the total number of files that can be opened.
|
|
*/
|
|
error = -EMFILE;
|
|
if (fd >= end)
|
|
goto out;
|
|
|
|
error = expand_files(files, fd);
|
|
if (error < 0)
|
|
goto out;
|
|
|
|
/*
|
|
* If we needed to expand the fs array we
|
|
* might have blocked - try again.
|
|
*/
|
|
if (error)
|
|
goto repeat;
|
|
|
|
if (start <= files->next_fd)
|
|
files->next_fd = fd + 1;
|
|
|
|
__set_open_fd(fd, fdt);
|
|
if (flags & O_CLOEXEC)
|
|
__set_close_on_exec(fd, fdt);
|
|
else
|
|
__clear_close_on_exec(fd, fdt);
|
|
error = fd;
|
|
#if 1
|
|
/* Sanity check */
|
|
if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
|
|
printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
|
|
rcu_assign_pointer(fdt->fd[fd], NULL);
|
|
}
|
|
#endif
|
|
|
|
out:
|
|
spin_unlock(&files->file_lock);
|
|
return error;
|
|
}
|
|
|
|
int __get_unused_fd_flags(unsigned flags, unsigned long nofile)
|
|
{
|
|
return alloc_fd(0, nofile, flags);
|
|
}
|
|
|
|
int get_unused_fd_flags(unsigned flags)
|
|
{
|
|
return __get_unused_fd_flags(flags, rlimit(RLIMIT_NOFILE));
|
|
}
|
|
EXPORT_SYMBOL(get_unused_fd_flags);
|
|
|
|
static void __put_unused_fd(struct files_struct *files, unsigned int fd)
|
|
{
|
|
struct fdtable *fdt = files_fdtable(files);
|
|
__clear_open_fd(fd, fdt);
|
|
if (fd < files->next_fd)
|
|
files->next_fd = fd;
|
|
}
|
|
|
|
void put_unused_fd(unsigned int fd)
|
|
{
|
|
struct files_struct *files = current->files;
|
|
spin_lock(&files->file_lock);
|
|
__put_unused_fd(files, fd);
|
|
spin_unlock(&files->file_lock);
|
|
}
|
|
|
|
EXPORT_SYMBOL(put_unused_fd);
|
|
|
|
/*
|
|
* Install a file pointer in the fd array.
|
|
*
|
|
* The VFS is full of places where we drop the files lock between
|
|
* setting the open_fds bitmap and installing the file in the file
|
|
* array. At any such point, we are vulnerable to a dup2() race
|
|
* installing a file in the array before us. We need to detect this and
|
|
* fput() the struct file we are about to overwrite in this case.
|
|
*
|
|
* It should never happen - if we allow dup2() do it, _really_ bad things
|
|
* will follow.
|
|
*
|
|
* This consumes the "file" refcount, so callers should treat it
|
|
* as if they had called fput(file).
|
|
*/
|
|
|
|
void fd_install(unsigned int fd, struct file *file)
|
|
{
|
|
struct files_struct *files = current->files;
|
|
struct fdtable *fdt;
|
|
|
|
rcu_read_lock_sched();
|
|
|
|
if (unlikely(files->resize_in_progress)) {
|
|
rcu_read_unlock_sched();
|
|
spin_lock(&files->file_lock);
|
|
fdt = files_fdtable(files);
|
|
BUG_ON(fdt->fd[fd] != NULL);
|
|
rcu_assign_pointer(fdt->fd[fd], file);
|
|
spin_unlock(&files->file_lock);
|
|
return;
|
|
}
|
|
/* coupled with smp_wmb() in expand_fdtable() */
|
|
smp_rmb();
|
|
fdt = rcu_dereference_sched(files->fdt);
|
|
BUG_ON(fdt->fd[fd] != NULL);
|
|
rcu_assign_pointer(fdt->fd[fd], file);
|
|
rcu_read_unlock_sched();
|
|
}
|
|
|
|
EXPORT_SYMBOL(fd_install);
|
|
|
|
/**
|
|
* pick_file - return file associatd with fd
|
|
* @files: file struct to retrieve file from
|
|
* @fd: file descriptor to retrieve file for
|
|
*
|
|
* If this functions returns an EINVAL error pointer the fd was beyond the
|
|
* current maximum number of file descriptors for that fdtable.
|
|
*
|
|
* Returns: The file associated with @fd, on error returns an error pointer.
|
|
*/
|
|
static struct file *pick_file(struct files_struct *files, unsigned fd)
|
|
{
|
|
struct file *file;
|
|
struct fdtable *fdt;
|
|
|
|
spin_lock(&files->file_lock);
|
|
fdt = files_fdtable(files);
|
|
if (fd >= fdt->max_fds) {
|
|
file = ERR_PTR(-EINVAL);
|
|
goto out_unlock;
|
|
}
|
|
file = fdt->fd[fd];
|
|
if (!file) {
|
|
file = ERR_PTR(-EBADF);
|
|
goto out_unlock;
|
|
}
|
|
rcu_assign_pointer(fdt->fd[fd], NULL);
|
|
__put_unused_fd(files, fd);
|
|
|
|
out_unlock:
|
|
spin_unlock(&files->file_lock);
|
|
return file;
|
|
}
|
|
|
|
int close_fd(unsigned fd)
|
|
{
|
|
struct files_struct *files = current->files;
|
|
struct file *file;
|
|
|
|
file = pick_file(files, fd);
|
|
if (IS_ERR(file))
|
|
return -EBADF;
|
|
|
|
return filp_close(file, files);
|
|
}
|
|
EXPORT_SYMBOL(close_fd); /* for ksys_close() */
|
|
|
|
/**
|
|
* last_fd - return last valid index into fd table
|
|
* @cur_fds: files struct
|
|
*
|
|
* Context: Either rcu read lock or files_lock must be held.
|
|
*
|
|
* Returns: Last valid index into fdtable.
|
|
*/
|
|
static inline unsigned last_fd(struct fdtable *fdt)
|
|
{
|
|
return fdt->max_fds - 1;
|
|
}
|
|
|
|
static inline void __range_cloexec(struct files_struct *cur_fds,
|
|
unsigned int fd, unsigned int max_fd)
|
|
{
|
|
struct fdtable *fdt;
|
|
|
|
/* make sure we're using the correct maximum value */
|
|
spin_lock(&cur_fds->file_lock);
|
|
fdt = files_fdtable(cur_fds);
|
|
max_fd = min(last_fd(fdt), max_fd);
|
|
if (fd <= max_fd)
|
|
bitmap_set(fdt->close_on_exec, fd, max_fd - fd + 1);
|
|
spin_unlock(&cur_fds->file_lock);
|
|
}
|
|
|
|
static inline void __range_close(struct files_struct *cur_fds, unsigned int fd,
|
|
unsigned int max_fd)
|
|
{
|
|
while (fd <= max_fd) {
|
|
struct file *file;
|
|
|
|
file = pick_file(cur_fds, fd++);
|
|
if (!IS_ERR(file)) {
|
|
/* found a valid file to close */
|
|
filp_close(file, cur_fds);
|
|
cond_resched();
|
|
continue;
|
|
}
|
|
|
|
/* beyond the last fd in that table */
|
|
if (PTR_ERR(file) == -EINVAL)
|
|
return;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* __close_range() - Close all file descriptors in a given range.
|
|
*
|
|
* @fd: starting file descriptor to close
|
|
* @max_fd: last file descriptor to close
|
|
*
|
|
* This closes a range of file descriptors. All file descriptors
|
|
* from @fd up to and including @max_fd are closed.
|
|
*/
|
|
int __close_range(unsigned fd, unsigned max_fd, unsigned int flags)
|
|
{
|
|
struct task_struct *me = current;
|
|
struct files_struct *cur_fds = me->files, *fds = NULL;
|
|
|
|
if (flags & ~(CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC))
|
|
return -EINVAL;
|
|
|
|
if (fd > max_fd)
|
|
return -EINVAL;
|
|
|
|
if (flags & CLOSE_RANGE_UNSHARE) {
|
|
int ret;
|
|
unsigned int max_unshare_fds = NR_OPEN_MAX;
|
|
|
|
/*
|
|
* If the caller requested all fds to be made cloexec we always
|
|
* copy all of the file descriptors since they still want to
|
|
* use them.
|
|
*/
|
|
if (!(flags & CLOSE_RANGE_CLOEXEC)) {
|
|
/*
|
|
* If the requested range is greater than the current
|
|
* maximum, we're closing everything so only copy all
|
|
* file descriptors beneath the lowest file descriptor.
|
|
*/
|
|
rcu_read_lock();
|
|
if (max_fd >= last_fd(files_fdtable(cur_fds)))
|
|
max_unshare_fds = fd;
|
|
rcu_read_unlock();
|
|
}
|
|
|
|
ret = unshare_fd(CLONE_FILES, max_unshare_fds, &fds);
|
|
if (ret)
|
|
return ret;
|
|
|
|
/*
|
|
* We used to share our file descriptor table, and have now
|
|
* created a private one, make sure we're using it below.
|
|
*/
|
|
if (fds)
|
|
swap(cur_fds, fds);
|
|
}
|
|
|
|
if (flags & CLOSE_RANGE_CLOEXEC)
|
|
__range_cloexec(cur_fds, fd, max_fd);
|
|
else
|
|
__range_close(cur_fds, fd, max_fd);
|
|
|
|
if (fds) {
|
|
/*
|
|
* We're done closing the files we were supposed to. Time to install
|
|
* the new file descriptor table and drop the old one.
|
|
*/
|
|
task_lock(me);
|
|
me->files = cur_fds;
|
|
task_unlock(me);
|
|
put_files_struct(fds);
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* See close_fd_get_file() below, this variant assumes current->files->file_lock
|
|
* is held.
|
|
*/
|
|
int __close_fd_get_file(unsigned int fd, struct file **res)
|
|
{
|
|
struct files_struct *files = current->files;
|
|
struct file *file;
|
|
struct fdtable *fdt;
|
|
|
|
fdt = files_fdtable(files);
|
|
if (fd >= fdt->max_fds)
|
|
goto out_err;
|
|
file = fdt->fd[fd];
|
|
if (!file)
|
|
goto out_err;
|
|
rcu_assign_pointer(fdt->fd[fd], NULL);
|
|
__put_unused_fd(files, fd);
|
|
get_file(file);
|
|
*res = file;
|
|
return 0;
|
|
out_err:
|
|
*res = NULL;
|
|
return -ENOENT;
|
|
}
|
|
|
|
/*
|
|
* variant of close_fd that gets a ref on the file for later fput.
|
|
* The caller must ensure that filp_close() called on the file, and then
|
|
* an fput().
|
|
*/
|
|
int close_fd_get_file(unsigned int fd, struct file **res)
|
|
{
|
|
struct files_struct *files = current->files;
|
|
int ret;
|
|
|
|
spin_lock(&files->file_lock);
|
|
ret = __close_fd_get_file(fd, res);
|
|
spin_unlock(&files->file_lock);
|
|
|
|
return ret;
|
|
}
|
|
|
|
void do_close_on_exec(struct files_struct *files)
|
|
{
|
|
unsigned i;
|
|
struct fdtable *fdt;
|
|
|
|
/* exec unshares first */
|
|
spin_lock(&files->file_lock);
|
|
for (i = 0; ; i++) {
|
|
unsigned long set;
|
|
unsigned fd = i * BITS_PER_LONG;
|
|
fdt = files_fdtable(files);
|
|
if (fd >= fdt->max_fds)
|
|
break;
|
|
set = fdt->close_on_exec[i];
|
|
if (!set)
|
|
continue;
|
|
fdt->close_on_exec[i] = 0;
|
|
for ( ; set ; fd++, set >>= 1) {
|
|
struct file *file;
|
|
if (!(set & 1))
|
|
continue;
|
|
file = fdt->fd[fd];
|
|
if (!file)
|
|
continue;
|
|
rcu_assign_pointer(fdt->fd[fd], NULL);
|
|
__put_unused_fd(files, fd);
|
|
spin_unlock(&files->file_lock);
|
|
filp_close(file, files);
|
|
cond_resched();
|
|
spin_lock(&files->file_lock);
|
|
}
|
|
|
|
}
|
|
spin_unlock(&files->file_lock);
|
|
}
|
|
|
|
static inline struct file *__fget_files_rcu(struct files_struct *files,
|
|
unsigned int fd, fmode_t mask, unsigned int refs)
|
|
{
|
|
for (;;) {
|
|
struct file *file;
|
|
struct fdtable *fdt = rcu_dereference_raw(files->fdt);
|
|
struct file __rcu **fdentry;
|
|
|
|
if (unlikely(fd >= fdt->max_fds))
|
|
return NULL;
|
|
|
|
fdentry = fdt->fd + array_index_nospec(fd, fdt->max_fds);
|
|
file = rcu_dereference_raw(*fdentry);
|
|
if (unlikely(!file))
|
|
return NULL;
|
|
|
|
if (unlikely(file->f_mode & mask))
|
|
return NULL;
|
|
|
|
/*
|
|
* Ok, we have a file pointer. However, because we do
|
|
* this all locklessly under RCU, we may be racing with
|
|
* that file being closed.
|
|
*
|
|
* Such a race can take two forms:
|
|
*
|
|
* (a) the file ref already went down to zero,
|
|
* and get_file_rcu_many() fails. Just try
|
|
* again:
|
|
*/
|
|
if (unlikely(!get_file_rcu_many(file, refs)))
|
|
continue;
|
|
|
|
/*
|
|
* (b) the file table entry has changed under us.
|
|
* Note that we don't need to re-check the 'fdt->fd'
|
|
* pointer having changed, because it always goes
|
|
* hand-in-hand with 'fdt'.
|
|
*
|
|
* If so, we need to put our refs and try again.
|
|
*/
|
|
if (unlikely(rcu_dereference_raw(files->fdt) != fdt) ||
|
|
unlikely(rcu_dereference_raw(*fdentry) != file)) {
|
|
fput_many(file, refs);
|
|
continue;
|
|
}
|
|
|
|
/*
|
|
* Ok, we have a ref to the file, and checked that it
|
|
* still exists.
|
|
*/
|
|
return file;
|
|
}
|
|
}
|
|
|
|
static struct file *__fget_files(struct files_struct *files, unsigned int fd,
|
|
fmode_t mask, unsigned int refs)
|
|
{
|
|
struct file *file;
|
|
|
|
rcu_read_lock();
|
|
file = __fget_files_rcu(files, fd, mask, refs);
|
|
rcu_read_unlock();
|
|
|
|
return file;
|
|
}
|
|
|
|
static inline struct file *__fget(unsigned int fd, fmode_t mask,
|
|
unsigned int refs)
|
|
{
|
|
return __fget_files(current->files, fd, mask, refs);
|
|
}
|
|
|
|
struct file *fget_many(unsigned int fd, unsigned int refs)
|
|
{
|
|
return __fget(fd, FMODE_PATH, refs);
|
|
}
|
|
|
|
struct file *fget(unsigned int fd)
|
|
{
|
|
return __fget(fd, FMODE_PATH, 1);
|
|
}
|
|
EXPORT_SYMBOL(fget);
|
|
|
|
struct file *fget_raw(unsigned int fd)
|
|
{
|
|
return __fget(fd, 0, 1);
|
|
}
|
|
EXPORT_SYMBOL(fget_raw);
|
|
|
|
struct file *fget_task(struct task_struct *task, unsigned int fd)
|
|
{
|
|
struct file *file = NULL;
|
|
|
|
task_lock(task);
|
|
if (task->files)
|
|
file = __fget_files(task->files, fd, 0, 1);
|
|
task_unlock(task);
|
|
|
|
return file;
|
|
}
|
|
|
|
struct file *task_lookup_fd_rcu(struct task_struct *task, unsigned int fd)
|
|
{
|
|
/* Must be called with rcu_read_lock held */
|
|
struct files_struct *files;
|
|
struct file *file = NULL;
|
|
|
|
task_lock(task);
|
|
files = task->files;
|
|
if (files)
|
|
file = files_lookup_fd_rcu(files, fd);
|
|
task_unlock(task);
|
|
|
|
return file;
|
|
}
|
|
|
|
struct file *task_lookup_next_fd_rcu(struct task_struct *task, unsigned int *ret_fd)
|
|
{
|
|
/* Must be called with rcu_read_lock held */
|
|
struct files_struct *files;
|
|
unsigned int fd = *ret_fd;
|
|
struct file *file = NULL;
|
|
|
|
task_lock(task);
|
|
files = task->files;
|
|
if (files) {
|
|
for (; fd < files_fdtable(files)->max_fds; fd++) {
|
|
file = files_lookup_fd_rcu(files, fd);
|
|
if (file)
|
|
break;
|
|
}
|
|
}
|
|
task_unlock(task);
|
|
*ret_fd = fd;
|
|
return file;
|
|
}
|
|
|
|
/*
|
|
* Lightweight file lookup - no refcnt increment if fd table isn't shared.
|
|
*
|
|
* You can use this instead of fget if you satisfy all of the following
|
|
* conditions:
|
|
* 1) You must call fput_light before exiting the syscall and returning control
|
|
* to userspace (i.e. you cannot remember the returned struct file * after
|
|
* returning to userspace).
|
|
* 2) You must not call filp_close on the returned struct file * in between
|
|
* calls to fget_light and fput_light.
|
|
* 3) You must not clone the current task in between the calls to fget_light
|
|
* and fput_light.
|
|
*
|
|
* The fput_needed flag returned by fget_light should be passed to the
|
|
* corresponding fput_light.
|
|
*/
|
|
static unsigned long __fget_light(unsigned int fd, fmode_t mask)
|
|
{
|
|
struct files_struct *files = current->files;
|
|
struct file *file;
|
|
|
|
if (atomic_read(&files->count) == 1) {
|
|
file = files_lookup_fd_raw(files, fd);
|
|
if (!file || unlikely(file->f_mode & mask))
|
|
return 0;
|
|
return (unsigned long)file;
|
|
} else {
|
|
file = __fget(fd, mask, 1);
|
|
if (!file)
|
|
return 0;
|
|
return FDPUT_FPUT | (unsigned long)file;
|
|
}
|
|
}
|
|
unsigned long __fdget(unsigned int fd)
|
|
{
|
|
return __fget_light(fd, FMODE_PATH);
|
|
}
|
|
EXPORT_SYMBOL(__fdget);
|
|
|
|
unsigned long __fdget_raw(unsigned int fd)
|
|
{
|
|
return __fget_light(fd, 0);
|
|
}
|
|
|
|
unsigned long __fdget_pos(unsigned int fd)
|
|
{
|
|
unsigned long v = __fdget(fd);
|
|
struct file *file = (struct file *)(v & ~3);
|
|
|
|
if (file && (file->f_mode & FMODE_ATOMIC_POS)) {
|
|
if (file_count(file) > 1) {
|
|
v |= FDPUT_POS_UNLOCK;
|
|
mutex_lock(&file->f_pos_lock);
|
|
}
|
|
}
|
|
return v;
|
|
}
|
|
|
|
void __f_unlock_pos(struct file *f)
|
|
{
|
|
mutex_unlock(&f->f_pos_lock);
|
|
}
|
|
|
|
/*
|
|
* We only lock f_pos if we have threads or if the file might be
|
|
* shared with another process. In both cases we'll have an elevated
|
|
* file count (done either by fdget() or by fork()).
|
|
*/
|
|
|
|
void set_close_on_exec(unsigned int fd, int flag)
|
|
{
|
|
struct files_struct *files = current->files;
|
|
struct fdtable *fdt;
|
|
spin_lock(&files->file_lock);
|
|
fdt = files_fdtable(files);
|
|
if (flag)
|
|
__set_close_on_exec(fd, fdt);
|
|
else
|
|
__clear_close_on_exec(fd, fdt);
|
|
spin_unlock(&files->file_lock);
|
|
}
|
|
|
|
bool get_close_on_exec(unsigned int fd)
|
|
{
|
|
struct files_struct *files = current->files;
|
|
struct fdtable *fdt;
|
|
bool res;
|
|
rcu_read_lock();
|
|
fdt = files_fdtable(files);
|
|
res = close_on_exec(fd, fdt);
|
|
rcu_read_unlock();
|
|
return res;
|
|
}
|
|
|
|
static int do_dup2(struct files_struct *files,
|
|
struct file *file, unsigned fd, unsigned flags)
|
|
__releases(&files->file_lock)
|
|
{
|
|
struct file *tofree;
|
|
struct fdtable *fdt;
|
|
|
|
/*
|
|
* We need to detect attempts to do dup2() over allocated but still
|
|
* not finished descriptor. NB: OpenBSD avoids that at the price of
|
|
* extra work in their equivalent of fget() - they insert struct
|
|
* file immediately after grabbing descriptor, mark it larval if
|
|
* more work (e.g. actual opening) is needed and make sure that
|
|
* fget() treats larval files as absent. Potentially interesting,
|
|
* but while extra work in fget() is trivial, locking implications
|
|
* and amount of surgery on open()-related paths in VFS are not.
|
|
* FreeBSD fails with -EBADF in the same situation, NetBSD "solution"
|
|
* deadlocks in rather amusing ways, AFAICS. All of that is out of
|
|
* scope of POSIX or SUS, since neither considers shared descriptor
|
|
* tables and this condition does not arise without those.
|
|
*/
|
|
fdt = files_fdtable(files);
|
|
tofree = fdt->fd[fd];
|
|
if (!tofree && fd_is_open(fd, fdt))
|
|
goto Ebusy;
|
|
get_file(file);
|
|
rcu_assign_pointer(fdt->fd[fd], file);
|
|
__set_open_fd(fd, fdt);
|
|
if (flags & O_CLOEXEC)
|
|
__set_close_on_exec(fd, fdt);
|
|
else
|
|
__clear_close_on_exec(fd, fdt);
|
|
spin_unlock(&files->file_lock);
|
|
|
|
if (tofree)
|
|
filp_close(tofree, files);
|
|
|
|
return fd;
|
|
|
|
Ebusy:
|
|
spin_unlock(&files->file_lock);
|
|
return -EBUSY;
|
|
}
|
|
|
|
int replace_fd(unsigned fd, struct file *file, unsigned flags)
|
|
{
|
|
int err;
|
|
struct files_struct *files = current->files;
|
|
|
|
if (!file)
|
|
return close_fd(fd);
|
|
|
|
if (fd >= rlimit(RLIMIT_NOFILE))
|
|
return -EBADF;
|
|
|
|
spin_lock(&files->file_lock);
|
|
err = expand_files(files, fd);
|
|
if (unlikely(err < 0))
|
|
goto out_unlock;
|
|
return do_dup2(files, file, fd, flags);
|
|
|
|
out_unlock:
|
|
spin_unlock(&files->file_lock);
|
|
return err;
|
|
}
|
|
|
|
/**
|
|
* __receive_fd() - Install received file into file descriptor table
|
|
* @file: struct file that was received from another process
|
|
* @ufd: __user pointer to write new fd number to
|
|
* @o_flags: the O_* flags to apply to the new fd entry
|
|
*
|
|
* Installs a received file into the file descriptor table, with appropriate
|
|
* checks and count updates. Optionally writes the fd number to userspace, if
|
|
* @ufd is non-NULL.
|
|
*
|
|
* This helper handles its own reference counting of the incoming
|
|
* struct file.
|
|
*
|
|
* Returns newly install fd or -ve on error.
|
|
*/
|
|
int __receive_fd(struct file *file, int __user *ufd, unsigned int o_flags)
|
|
{
|
|
int new_fd;
|
|
int error;
|
|
|
|
error = security_file_receive(file);
|
|
if (error)
|
|
return error;
|
|
|
|
new_fd = get_unused_fd_flags(o_flags);
|
|
if (new_fd < 0)
|
|
return new_fd;
|
|
|
|
if (ufd) {
|
|
error = put_user(new_fd, ufd);
|
|
if (error) {
|
|
put_unused_fd(new_fd);
|
|
return error;
|
|
}
|
|
}
|
|
|
|
fd_install(new_fd, get_file(file));
|
|
__receive_sock(file);
|
|
return new_fd;
|
|
}
|
|
|
|
int receive_fd_replace(int new_fd, struct file *file, unsigned int o_flags)
|
|
{
|
|
int error;
|
|
|
|
error = security_file_receive(file);
|
|
if (error)
|
|
return error;
|
|
error = replace_fd(new_fd, file, o_flags);
|
|
if (error)
|
|
return error;
|
|
__receive_sock(file);
|
|
return new_fd;
|
|
}
|
|
|
|
int receive_fd(struct file *file, unsigned int o_flags)
|
|
{
|
|
return __receive_fd(file, NULL, o_flags);
|
|
}
|
|
EXPORT_SYMBOL_GPL(receive_fd);
|
|
|
|
static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
|
|
{
|
|
int err = -EBADF;
|
|
struct file *file;
|
|
struct files_struct *files = current->files;
|
|
|
|
if ((flags & ~O_CLOEXEC) != 0)
|
|
return -EINVAL;
|
|
|
|
if (unlikely(oldfd == newfd))
|
|
return -EINVAL;
|
|
|
|
if (newfd >= rlimit(RLIMIT_NOFILE))
|
|
return -EBADF;
|
|
|
|
spin_lock(&files->file_lock);
|
|
err = expand_files(files, newfd);
|
|
file = files_lookup_fd_locked(files, oldfd);
|
|
if (unlikely(!file))
|
|
goto Ebadf;
|
|
if (unlikely(err < 0)) {
|
|
if (err == -EMFILE)
|
|
goto Ebadf;
|
|
goto out_unlock;
|
|
}
|
|
return do_dup2(files, file, newfd, flags);
|
|
|
|
Ebadf:
|
|
err = -EBADF;
|
|
out_unlock:
|
|
spin_unlock(&files->file_lock);
|
|
return err;
|
|
}
|
|
|
|
SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
|
|
{
|
|
return ksys_dup3(oldfd, newfd, flags);
|
|
}
|
|
|
|
SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
|
|
{
|
|
if (unlikely(newfd == oldfd)) { /* corner case */
|
|
struct files_struct *files = current->files;
|
|
int retval = oldfd;
|
|
|
|
rcu_read_lock();
|
|
if (!files_lookup_fd_rcu(files, oldfd))
|
|
retval = -EBADF;
|
|
rcu_read_unlock();
|
|
return retval;
|
|
}
|
|
return ksys_dup3(oldfd, newfd, 0);
|
|
}
|
|
|
|
SYSCALL_DEFINE1(dup, unsigned int, fildes)
|
|
{
|
|
int ret = -EBADF;
|
|
struct file *file = fget_raw(fildes);
|
|
|
|
if (file) {
|
|
ret = get_unused_fd_flags(0);
|
|
if (ret >= 0)
|
|
fd_install(ret, file);
|
|
else
|
|
fput(file);
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
int f_dupfd(unsigned int from, struct file *file, unsigned flags)
|
|
{
|
|
unsigned long nofile = rlimit(RLIMIT_NOFILE);
|
|
int err;
|
|
if (from >= nofile)
|
|
return -EINVAL;
|
|
err = alloc_fd(from, nofile, flags);
|
|
if (err >= 0) {
|
|
get_file(file);
|
|
fd_install(err, file);
|
|
}
|
|
return err;
|
|
}
|
|
|
|
int iterate_fd(struct files_struct *files, unsigned n,
|
|
int (*f)(const void *, struct file *, unsigned),
|
|
const void *p)
|
|
{
|
|
struct fdtable *fdt;
|
|
int res = 0;
|
|
if (!files)
|
|
return 0;
|
|
spin_lock(&files->file_lock);
|
|
for (fdt = files_fdtable(files); n < fdt->max_fds; n++) {
|
|
struct file *file;
|
|
file = rcu_dereference_check_fdtable(files, fdt->fd[n]);
|
|
if (!file)
|
|
continue;
|
|
res = f(p, file, n);
|
|
if (res)
|
|
break;
|
|
}
|
|
spin_unlock(&files->file_lock);
|
|
return res;
|
|
}
|
|
EXPORT_SYMBOL(iterate_fd);
|