linux-stable/fs/file.c
Christian Brauner 4e94ddfe2a
file: remove __receive_fd()
Honestly, there's little value in having a helper with and without that
int __user *ufd argument. It's just messy and doesn't really give us
anything. Just expose receive_fd() with that argument and get rid of
that helper.

Link: https://lore.kernel.org/r/20231130-vfs-files-fixes-v1-5-e73ca6f4ea83@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>
2023-12-12 14:24:14 +01:00

1462 lines
36 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* linux/fs/file.c
*
* Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
*
* Manage the dynamic fd arrays in the process files_struct.
*/
#include <linux/syscalls.h>
#include <linux/export.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/bitops.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/close_range.h>
#include <net/sock.h>
#include "internal.h"
unsigned int sysctl_nr_open __read_mostly = 1024*1024;
unsigned int sysctl_nr_open_min = BITS_PER_LONG;
/* our min() is unusable in constant expressions ;-/ */
#define __const_min(x, y) ((x) < (y) ? (x) : (y))
unsigned int sysctl_nr_open_max =
__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;
static void __free_fdtable(struct fdtable *fdt)
{
kvfree(fdt->fd);
kvfree(fdt->open_fds);
kfree(fdt);
}
static void free_fdtable_rcu(struct rcu_head *rcu)
{
__free_fdtable(container_of(rcu, struct fdtable, rcu));
}
#define BITBIT_NR(nr) BITS_TO_LONGS(BITS_TO_LONGS(nr))
#define BITBIT_SIZE(nr) (BITBIT_NR(nr) * sizeof(long))
/*
* Copy 'count' fd bits from the old table to the new table and clear the extra
* space if any. This does not copy the file pointers. Called with the files
* spinlock held for write.
*/
static void copy_fd_bitmaps(struct fdtable *nfdt, struct fdtable *ofdt,
unsigned int count)
{
unsigned int cpy, set;
cpy = count / BITS_PER_BYTE;
set = (nfdt->max_fds - count) / BITS_PER_BYTE;
memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
memset((char *)nfdt->open_fds + cpy, 0, set);
memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
memset((char *)nfdt->close_on_exec + cpy, 0, set);
cpy = BITBIT_SIZE(count);
set = BITBIT_SIZE(nfdt->max_fds) - cpy;
memcpy(nfdt->full_fds_bits, ofdt->full_fds_bits, cpy);
memset((char *)nfdt->full_fds_bits + cpy, 0, set);
}
/*
* Copy all file descriptors from the old table to the new, expanded table and
* clear the extra space. Called with the files spinlock held for write.
*/
static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
{
size_t cpy, set;
BUG_ON(nfdt->max_fds < ofdt->max_fds);
cpy = ofdt->max_fds * sizeof(struct file *);
set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
memcpy(nfdt->fd, ofdt->fd, cpy);
memset((char *)nfdt->fd + cpy, 0, set);
copy_fd_bitmaps(nfdt, ofdt, ofdt->max_fds);
}
/*
* Note how the fdtable bitmap allocations very much have to be a multiple of
* BITS_PER_LONG. This is not only because we walk those things in chunks of
* 'unsigned long' in some places, but simply because that is how the Linux
* kernel bitmaps are defined to work: they are not "bits in an array of bytes",
* they are very much "bits in an array of unsigned long".
*
* The ALIGN(nr, BITS_PER_LONG) here is for clarity: since we just multiplied
* by that "1024/sizeof(ptr)" before, we already know there are sufficient
* clear low bits. Clang seems to realize that, gcc ends up being confused.
*
* On a 128-bit machine, the ALIGN() would actually matter. In the meantime,
* let's consider it documentation (and maybe a test-case for gcc to improve
* its code generation ;)
*/
static struct fdtable * alloc_fdtable(unsigned int nr)
{
struct fdtable *fdt;
void *data;
/*
* Figure out how many fds we actually want to support in this fdtable.
* Allocation steps are keyed to the size of the fdarray, since it
* grows far faster than any of the other dynamic data. We try to fit
* the fdarray into comfortable page-tuned chunks: starting at 1024B
* and growing in powers of two from there on.
*/
nr /= (1024 / sizeof(struct file *));
nr = roundup_pow_of_two(nr + 1);
nr *= (1024 / sizeof(struct file *));
nr = ALIGN(nr, BITS_PER_LONG);
/*
* Note that this can drive nr *below* what we had passed if sysctl_nr_open
* had been set lower between the check in expand_files() and here. Deal
* with that in caller, it's cheaper that way.
*
* We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
* bitmaps handling below becomes unpleasant, to put it mildly...
*/
if (unlikely(nr > sysctl_nr_open))
nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL_ACCOUNT);
if (!fdt)
goto out;
fdt->max_fds = nr;
data = kvmalloc_array(nr, sizeof(struct file *), GFP_KERNEL_ACCOUNT);
if (!data)
goto out_fdt;
fdt->fd = data;
data = kvmalloc(max_t(size_t,
2 * nr / BITS_PER_BYTE + BITBIT_SIZE(nr), L1_CACHE_BYTES),
GFP_KERNEL_ACCOUNT);
if (!data)
goto out_arr;
fdt->open_fds = data;
data += nr / BITS_PER_BYTE;
fdt->close_on_exec = data;
data += nr / BITS_PER_BYTE;
fdt->full_fds_bits = data;
return fdt;
out_arr:
kvfree(fdt->fd);
out_fdt:
kfree(fdt);
out:
return NULL;
}
/*
* Expand the file descriptor table.
* This function will allocate a new fdtable and both fd array and fdset, of
* the given size.
* Return <0 error code on error; 1 on successful completion.
* The files->file_lock should be held on entry, and will be held on exit.
*/
static int expand_fdtable(struct files_struct *files, unsigned int nr)
__releases(files->file_lock)
__acquires(files->file_lock)
{
struct fdtable *new_fdt, *cur_fdt;
spin_unlock(&files->file_lock);
new_fdt = alloc_fdtable(nr);
/* make sure all fd_install() have seen resize_in_progress
* or have finished their rcu_read_lock_sched() section.
*/
if (atomic_read(&files->count) > 1)
synchronize_rcu();
spin_lock(&files->file_lock);
if (!new_fdt)
return -ENOMEM;
/*
* extremely unlikely race - sysctl_nr_open decreased between the check in
* caller and alloc_fdtable(). Cheaper to catch it here...
*/
if (unlikely(new_fdt->max_fds <= nr)) {
__free_fdtable(new_fdt);
return -EMFILE;
}
cur_fdt = files_fdtable(files);
BUG_ON(nr < cur_fdt->max_fds);
copy_fdtable(new_fdt, cur_fdt);
rcu_assign_pointer(files->fdt, new_fdt);
if (cur_fdt != &files->fdtab)
call_rcu(&cur_fdt->rcu, free_fdtable_rcu);
/* coupled with smp_rmb() in fd_install() */
smp_wmb();
return 1;
}
/*
* Expand files.
* This function will expand the file structures, if the requested size exceeds
* the current capacity and there is room for expansion.
* Return <0 error code on error; 0 when nothing done; 1 when files were
* expanded and execution may have blocked.
* The files->file_lock should be held on entry, and will be held on exit.
*/
static int expand_files(struct files_struct *files, unsigned int nr)
__releases(files->file_lock)
__acquires(files->file_lock)
{
struct fdtable *fdt;
int expanded = 0;
repeat:
fdt = files_fdtable(files);
/* Do we need to expand? */
if (nr < fdt->max_fds)
return expanded;
/* Can we expand? */
if (nr >= sysctl_nr_open)
return -EMFILE;
if (unlikely(files->resize_in_progress)) {
spin_unlock(&files->file_lock);
expanded = 1;
wait_event(files->resize_wait, !files->resize_in_progress);
spin_lock(&files->file_lock);
goto repeat;
}
/* All good, so we try */
files->resize_in_progress = true;
expanded = expand_fdtable(files, nr);
files->resize_in_progress = false;
wake_up_all(&files->resize_wait);
return expanded;
}
static inline void __set_close_on_exec(unsigned int fd, struct fdtable *fdt)
{
__set_bit(fd, fdt->close_on_exec);
}
static inline void __clear_close_on_exec(unsigned int fd, struct fdtable *fdt)
{
if (test_bit(fd, fdt->close_on_exec))
__clear_bit(fd, fdt->close_on_exec);
}
static inline void __set_open_fd(unsigned int fd, struct fdtable *fdt)
{
__set_bit(fd, fdt->open_fds);
fd /= BITS_PER_LONG;
if (!~fdt->open_fds[fd])
__set_bit(fd, fdt->full_fds_bits);
}
static inline void __clear_open_fd(unsigned int fd, struct fdtable *fdt)
{
__clear_bit(fd, fdt->open_fds);
__clear_bit(fd / BITS_PER_LONG, fdt->full_fds_bits);
}
static unsigned int count_open_files(struct fdtable *fdt)
{
unsigned int size = fdt->max_fds;
unsigned int i;
/* Find the last open fd */
for (i = size / BITS_PER_LONG; i > 0; ) {
if (fdt->open_fds[--i])
break;
}
i = (i + 1) * BITS_PER_LONG;
return i;
}
/*
* Note that a sane fdtable size always has to be a multiple of
* BITS_PER_LONG, since we have bitmaps that are sized by this.
*
* 'max_fds' will normally already be properly aligned, but it
* turns out that in the close_range() -> __close_range() ->
* unshare_fd() -> dup_fd() -> sane_fdtable_size() we can end
* up having a 'max_fds' value that isn't already aligned.
*
* Rather than make close_range() have to worry about this,
* just make that BITS_PER_LONG alignment be part of a sane
* fdtable size. Becuase that's really what it is.
*/
static unsigned int sane_fdtable_size(struct fdtable *fdt, unsigned int max_fds)
{
unsigned int count;
count = count_open_files(fdt);
if (max_fds < NR_OPEN_DEFAULT)
max_fds = NR_OPEN_DEFAULT;
return ALIGN(min(count, max_fds), BITS_PER_LONG);
}
/*
* Allocate a new files structure and copy contents from the
* passed in files structure.
* errorp will be valid only when the returned files_struct is NULL.
*/
struct files_struct *dup_fd(struct files_struct *oldf, unsigned int max_fds, int *errorp)
{
struct files_struct *newf;
struct file **old_fds, **new_fds;
unsigned int open_files, i;
struct fdtable *old_fdt, *new_fdt;
*errorp = -ENOMEM;
newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
if (!newf)
goto out;
atomic_set(&newf->count, 1);
spin_lock_init(&newf->file_lock);
newf->resize_in_progress = false;
init_waitqueue_head(&newf->resize_wait);
newf->next_fd = 0;
new_fdt = &newf->fdtab;
new_fdt->max_fds = NR_OPEN_DEFAULT;
new_fdt->close_on_exec = newf->close_on_exec_init;
new_fdt->open_fds = newf->open_fds_init;
new_fdt->full_fds_bits = newf->full_fds_bits_init;
new_fdt->fd = &newf->fd_array[0];
spin_lock(&oldf->file_lock);
old_fdt = files_fdtable(oldf);
open_files = sane_fdtable_size(old_fdt, max_fds);
/*
* Check whether we need to allocate a larger fd array and fd set.
*/
while (unlikely(open_files > new_fdt->max_fds)) {
spin_unlock(&oldf->file_lock);
if (new_fdt != &newf->fdtab)
__free_fdtable(new_fdt);
new_fdt = alloc_fdtable(open_files - 1);
if (!new_fdt) {
*errorp = -ENOMEM;
goto out_release;
}
/* beyond sysctl_nr_open; nothing to do */
if (unlikely(new_fdt->max_fds < open_files)) {
__free_fdtable(new_fdt);
*errorp = -EMFILE;
goto out_release;
}
/*
* Reacquire the oldf lock and a pointer to its fd table
* who knows it may have a new bigger fd table. We need
* the latest pointer.
*/
spin_lock(&oldf->file_lock);
old_fdt = files_fdtable(oldf);
open_files = sane_fdtable_size(old_fdt, max_fds);
}
copy_fd_bitmaps(new_fdt, old_fdt, open_files);
old_fds = old_fdt->fd;
new_fds = new_fdt->fd;
for (i = open_files; i != 0; i--) {
struct file *f = *old_fds++;
if (f) {
get_file(f);
} else {
/*
* The fd may be claimed in the fd bitmap but not yet
* instantiated in the files array if a sibling thread
* is partway through open(). So make sure that this
* fd is available to the new process.
*/
__clear_open_fd(open_files - i, new_fdt);
}
rcu_assign_pointer(*new_fds++, f);
}
spin_unlock(&oldf->file_lock);
/* clear the remainder */
memset(new_fds, 0, (new_fdt->max_fds - open_files) * sizeof(struct file *));
rcu_assign_pointer(newf->fdt, new_fdt);
return newf;
out_release:
kmem_cache_free(files_cachep, newf);
out:
return NULL;
}
static struct fdtable *close_files(struct files_struct * files)
{
/*
* It is safe to dereference the fd table without RCU or
* ->file_lock because this is the last reference to the
* files structure.
*/
struct fdtable *fdt = rcu_dereference_raw(files->fdt);
unsigned int i, j = 0;
for (;;) {
unsigned long set;
i = j * BITS_PER_LONG;
if (i >= fdt->max_fds)
break;
set = fdt->open_fds[j++];
while (set) {
if (set & 1) {
struct file * file = xchg(&fdt->fd[i], NULL);
if (file) {
filp_close(file, files);
cond_resched();
}
}
i++;
set >>= 1;
}
}
return fdt;
}
void put_files_struct(struct files_struct *files)
{
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);
kmem_cache_free(files_cachep, files);
}
}
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;
if (WARN_ON_ONCE(unlikely(file->f_mode & FMODE_BACKING)))
return;
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);
/**
* file_close_fd_locked - return file associated with fd
* @files: file struct to retrieve file from
* @fd: file descriptor to retrieve file for
*
* Doesn't take a separate reference count.
*
* Context: files_lock must be held.
*
* Returns: The file associated with @fd (NULL if @fd is not open)
*/
struct file *file_close_fd_locked(struct files_struct *files, unsigned fd)
{
struct fdtable *fdt = files_fdtable(files);
struct file *file;
lockdep_assert_held(&files->file_lock);
if (fd >= fdt->max_fds)
return NULL;
fd = array_index_nospec(fd, fdt->max_fds);
file = fdt->fd[fd];
if (file) {
rcu_assign_pointer(fdt->fd[fd], NULL);
__put_unused_fd(files, fd);
}
return file;
}
int close_fd(unsigned fd)
{
struct files_struct *files = current->files;
struct file *file;
spin_lock(&files->file_lock);
file = file_close_fd_locked(files, fd);
spin_unlock(&files->file_lock);
if (!file)
return -EBADF;
return filp_close(file, files);
}
EXPORT_SYMBOL(close_fd); /* for ksys_close() */
/**
* last_fd - return last valid index into fd table
* @fdt: File descriptor table.
*
* 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 *files, unsigned int fd,
unsigned int max_fd)
{
struct file *file;
unsigned n;
spin_lock(&files->file_lock);
n = last_fd(files_fdtable(files));
max_fd = min(max_fd, n);
for (; fd <= max_fd; fd++) {
file = file_close_fd_locked(files, fd);
if (file) {
spin_unlock(&files->file_lock);
filp_close(file, files);
cond_resched();
spin_lock(&files->file_lock);
} else if (need_resched()) {
spin_unlock(&files->file_lock);
cond_resched();
spin_lock(&files->file_lock);
}
}
spin_unlock(&files->file_lock);
}
/**
* __close_range() - Close all file descriptors in a given range.
*
* @fd: starting file descriptor to close
* @max_fd: last file descriptor to close
* @flags: CLOSE_RANGE flags.
*
* 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;
}
/**
* file_close_fd - return file associated with fd
* @fd: file descriptor to retrieve file for
*
* Doesn't take a separate reference count.
*
* Returns: The file associated with @fd (NULL if @fd is not open)
*/
struct file *file_close_fd(unsigned int fd)
{
struct files_struct *files = current->files;
struct file *file;
spin_lock(&files->file_lock);
file = file_close_fd_locked(files, fd);
spin_unlock(&files->file_lock);
return file;
}
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 struct file *__get_file_rcu(struct file __rcu **f)
{
struct file __rcu *file;
struct file __rcu *file_reloaded;
struct file __rcu *file_reloaded_cmp;
file = rcu_dereference_raw(*f);
if (!file)
return NULL;
if (unlikely(!atomic_long_inc_not_zero(&file->f_count)))
return ERR_PTR(-EAGAIN);
file_reloaded = rcu_dereference_raw(*f);
/*
* Ensure that all accesses have a dependency on the load from
* rcu_dereference_raw() above so we get correct ordering
* between reuse/allocation and the pointer check below.
*/
file_reloaded_cmp = file_reloaded;
OPTIMIZER_HIDE_VAR(file_reloaded_cmp);
/*
* atomic_long_inc_not_zero() above provided a full memory
* barrier when we acquired a reference.
*
* This is paired with the write barrier from assigning to the
* __rcu protected file pointer so that if that pointer still
* matches the current file, we know we have successfully
* acquired a reference to the right file.
*
* If the pointers don't match the file has been reallocated by
* SLAB_TYPESAFE_BY_RCU.
*/
if (file == file_reloaded_cmp)
return file_reloaded;
fput(file);
return ERR_PTR(-EAGAIN);
}
/**
* get_file_rcu - try go get a reference to a file under rcu
* @f: the file to get a reference on
*
* This function tries to get a reference on @f carefully verifying that
* @f hasn't been reused.
*
* This function should rarely have to be used and only by users who
* understand the implications of SLAB_TYPESAFE_BY_RCU. Try to avoid it.
*
* Return: Returns @f with the reference count increased or NULL.
*/
struct file *get_file_rcu(struct file __rcu **f)
{
for (;;) {
struct file __rcu *file;
file = __get_file_rcu(f);
if (unlikely(!file))
return NULL;
if (unlikely(IS_ERR(file)))
continue;
return file;
}
}
EXPORT_SYMBOL_GPL(get_file_rcu);
/**
* get_file_active - try go get a reference to a file
* @f: the file to get a reference on
*
* In contast to get_file_rcu() the pointer itself isn't part of the
* reference counting.
*
* This function should rarely have to be used and only by users who
* understand the implications of SLAB_TYPESAFE_BY_RCU. Try to avoid it.
*
* Return: Returns @f with the reference count increased or NULL.
*/
struct file *get_file_active(struct file **f)
{
struct file __rcu *file;
rcu_read_lock();
file = __get_file_rcu(f);
rcu_read_unlock();
if (IS_ERR(file))
file = NULL;
return file;
}
EXPORT_SYMBOL_GPL(get_file_active);
static inline struct file *__fget_files_rcu(struct files_struct *files,
unsigned int fd, fmode_t mask)
{
for (;;) {
struct file *file;
struct fdtable *fdt = rcu_dereference_raw(files->fdt);
struct file __rcu **fdentry;
unsigned long nospec_mask;
/* Mask is a 0 for invalid fd's, ~0 for valid ones */
nospec_mask = array_index_mask_nospec(fd, fdt->max_fds);
/*
* fdentry points to the 'fd' offset, or fdt->fd[0].
* Loading from fdt->fd[0] is always safe, because the
* array always exists.
*/
fdentry = fdt->fd + (fd & nospec_mask);
/* Do the load, then mask any invalid result */
file = rcu_dereference_raw(*fdentry);
file = (void *)(nospec_mask & (unsigned long)file);
if (unlikely(!file))
return NULL;
/*
* Ok, we have a file pointer that was valid at
* some point, but it might have become stale since.
*
* We need to confirm it by incrementing the refcount
* and then check the lookup again.
*
* atomic_long_inc_not_zero() gives us a full memory
* barrier. We only really need an 'acquire' one to
* protect the loads below, but we don't have that.
*/
if (unlikely(!atomic_long_inc_not_zero(&file->f_count)))
continue;
/*
* Such a race can take two forms:
*
* (a) the file ref already went down to zero and the
* file hasn't been reused yet or the file count
* isn't zero but the file has already been reused.
*
* (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 ref and try again.
*/
if (unlikely(file != rcu_dereference_raw(*fdentry)) ||
unlikely(rcu_dereference_raw(files->fdt) != fdt)) {
fput(file);
continue;
}
/*
* This isn't the file we're looking for or we're not
* allowed to get a reference to it.
*/
if (unlikely(file->f_mode & mask)) {
fput(file);
return NULL;
}
/*
* 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)
{
struct file *file;
rcu_read_lock();
file = __fget_files_rcu(files, fd, mask);
rcu_read_unlock();
return file;
}
static inline struct file *__fget(unsigned int fd, fmode_t mask)
{
return __fget_files(current->files, fd, mask);
}
struct file *fget(unsigned int fd)
{
return __fget(fd, FMODE_PATH);
}
EXPORT_SYMBOL(fget);
struct file *fget_raw(unsigned int fd)
{
return __fget(fd, 0);
}
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);
task_unlock(task);
return file;
}
struct file *lookup_fdget_rcu(unsigned int fd)
{
return __fget_files_rcu(current->files, fd, 0);
}
EXPORT_SYMBOL_GPL(lookup_fdget_rcu);
struct file *task_lookup_fdget_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 = __fget_files_rcu(files, fd, 0);
task_unlock(task);
return file;
}
struct file *task_lookup_next_fdget_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 = __fget_files_rcu(files, fd, 0);
if (file)
break;
}
}
task_unlock(task);
*ret_fd = fd;
return file;
}
EXPORT_SYMBOL(task_lookup_next_fdget_rcu);
/*
* 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 another thread is concurrently calling close_fd() followed
* by put_files_struct(), we must not observe the old table
* entry combined with the new refcount - otherwise we could
* return a file that is concurrently being freed.
*
* atomic_read_acquire() pairs with atomic_dec_and_test() in
* put_files_struct().
*/
if (likely(atomic_read_acquire(&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_files(files, fd, mask);
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);
}
/*
* Try to avoid f_pos locking. We only need it if the
* file is marked for FMODE_ATOMIC_POS, and it can be
* accessed multiple ways.
*
* Always do it for directories, because pidfd_getfd()
* can make a file accessible even if it otherwise would
* not be, and for directories this is a correctness
* issue, not a "POSIX requirement".
*/
static inline bool file_needs_f_pos_lock(struct file *file)
{
return (file->f_mode & FMODE_ATOMIC_POS) &&
(file_count(file) > 1 || file->f_op->iterate_shared);
}
unsigned long __fdget_pos(unsigned int fd)
{
unsigned long v = __fdget(fd);
struct file *file = (struct file *)(v & ~3);
if (file && file_needs_f_pos_lock(file)) {
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;
}
EXPORT_SYMBOL_GPL(receive_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;
}
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;
struct file *f;
int retval = oldfd;
rcu_read_lock();
f = __fget_files_rcu(files, oldfd, 0);
if (!f)
retval = -EBADF;
rcu_read_unlock();
if (f)
fput(f);
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);