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![Eric W. Biederman](/assets/img/avatar_default.png)
struct siginfo is a union and the kernel since 2.4 has been hiding a union tag in the high 16bits of si_code using the values: __SI_KILL __SI_TIMER __SI_POLL __SI_FAULT __SI_CHLD __SI_RT __SI_MESGQ __SI_SYS While this looks plausible on the surface, in practice this situation has not worked well. - Injected positive signals are not copied to user space properly unless they have these magic high bits set. - Injected positive signals are not reported properly by signalfd unless they have these magic high bits set. - These kernel internal values leaked to userspace via ptrace_peek_siginfo - It was possible to inject these kernel internal values and cause the the kernel to misbehave. - Kernel developers got confused and expected these kernel internal values in userspace in kernel self tests. - Kernel developers got confused and set si_code to __SI_FAULT which is SI_USER in userspace which causes userspace to think an ordinary user sent the signal and that it was not kernel generated. - The values make it impossible to reorganize the code to transform siginfo_copy_to_user into a plain copy_to_user. As si_code must be massaged before being passed to userspace. So remove these kernel internal si codes and make the kernel code simpler and more maintainable. To replace these kernel internal magic si_codes introduce the helper function siginfo_layout, that takes a signal number and an si_code and computes which union member of siginfo is being used. Have siginfo_layout return an enumeration so that gcc will have enough information to warn if a switch statement does not handle all of union members. A couple of architectures have a messed up ABI that defines signal specific duplications of SI_USER which causes more special cases in siginfo_layout than I would like. The good news is only problem architectures pay the cost. Update all of the code that used the previous magic __SI_ values to use the new SIL_ values and to call siginfo_layout to get those values. Escept where not all of the cases are handled remove the defaults in the switch statements so that if a new case is missed in the future the lack will show up at compile time. Modify the code that copies siginfo si_code to userspace to just copy the value and not cast si_code to a short first. The high bits are no longer used to hold a magic union member. Fixup the siginfo header files to stop including the __SI_ values in their constants and for the headers that were missing it to properly update the number of si_codes for each signal type. The fixes to copy_siginfo_from_user32 implementations has the interesting property that several of them perviously should never have worked as the __SI_ values they depended up where kernel internal. With that dependency gone those implementations should work much better. The idea of not passing the __SI_ values out to userspace and then not reinserting them has been tested with criu and criu worked without changes. Ref: 2.4.0-test1 Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
337 lines
8.9 KiB
C
337 lines
8.9 KiB
C
/*
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* fs/signalfd.c
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*
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* Copyright (C) 2003 Linus Torvalds
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*
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* Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
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* Changed ->read() to return a siginfo strcture instead of signal number.
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* Fixed locking in ->poll().
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* Added sighand-detach notification.
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* Added fd re-use in sys_signalfd() syscall.
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* Now using anonymous inode source.
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* Thanks to Oleg Nesterov for useful code review and suggestions.
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* More comments and suggestions from Arnd Bergmann.
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* Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
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* Retrieve multiple signals with one read() call
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* Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
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* Attach to the sighand only during read() and poll().
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*/
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#include <linux/file.h>
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#include <linux/poll.h>
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/kernel.h>
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#include <linux/signal.h>
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#include <linux/list.h>
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#include <linux/anon_inodes.h>
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#include <linux/signalfd.h>
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#include <linux/syscalls.h>
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#include <linux/proc_fs.h>
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#include <linux/compat.h>
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void signalfd_cleanup(struct sighand_struct *sighand)
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{
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wait_queue_head_t *wqh = &sighand->signalfd_wqh;
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/*
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* The lockless check can race with remove_wait_queue() in progress,
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* but in this case its caller should run under rcu_read_lock() and
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* sighand_cachep is SLAB_TYPESAFE_BY_RCU, we can safely return.
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*/
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if (likely(!waitqueue_active(wqh)))
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return;
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/* wait_queue_entry_t->func(POLLFREE) should do remove_wait_queue() */
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wake_up_poll(wqh, POLLHUP | POLLFREE);
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}
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struct signalfd_ctx {
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sigset_t sigmask;
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};
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static int signalfd_release(struct inode *inode, struct file *file)
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{
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kfree(file->private_data);
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return 0;
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}
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static unsigned int signalfd_poll(struct file *file, poll_table *wait)
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{
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struct signalfd_ctx *ctx = file->private_data;
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unsigned int events = 0;
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poll_wait(file, ¤t->sighand->signalfd_wqh, wait);
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spin_lock_irq(¤t->sighand->siglock);
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if (next_signal(¤t->pending, &ctx->sigmask) ||
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next_signal(¤t->signal->shared_pending,
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&ctx->sigmask))
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events |= POLLIN;
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spin_unlock_irq(¤t->sighand->siglock);
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return events;
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}
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/*
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* Copied from copy_siginfo_to_user() in kernel/signal.c
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*/
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static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
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siginfo_t const *kinfo)
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{
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long err;
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BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
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/*
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* Unused members should be zero ...
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*/
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err = __clear_user(uinfo, sizeof(*uinfo));
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/*
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* If you change siginfo_t structure, please be sure
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* this code is fixed accordingly.
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*/
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err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
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err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
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err |= __put_user(kinfo->si_code, &uinfo->ssi_code);
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switch (siginfo_layout(kinfo->si_signo, kinfo->si_code)) {
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case SIL_KILL:
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err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
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err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
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break;
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case SIL_TIMER:
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err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
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err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
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err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
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err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
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break;
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case SIL_POLL:
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err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
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err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
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break;
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case SIL_FAULT:
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err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
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#ifdef __ARCH_SI_TRAPNO
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err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
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#endif
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#ifdef BUS_MCEERR_AO
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/*
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* Other callers might not initialize the si_lsb field,
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* so check explicitly for the right codes here.
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*/
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if (kinfo->si_signo == SIGBUS &&
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(kinfo->si_code == BUS_MCEERR_AR ||
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kinfo->si_code == BUS_MCEERR_AO))
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err |= __put_user((short) kinfo->si_addr_lsb,
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&uinfo->ssi_addr_lsb);
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#endif
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break;
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case SIL_CHLD:
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err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
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err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
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err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
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err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
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err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
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break;
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case SIL_RT:
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default:
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/*
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* This case catches also the signals queued by sigqueue().
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*/
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err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
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err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
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err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
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err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
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break;
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}
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return err ? -EFAULT: sizeof(*uinfo);
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}
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static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
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int nonblock)
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{
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ssize_t ret;
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DECLARE_WAITQUEUE(wait, current);
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spin_lock_irq(¤t->sighand->siglock);
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ret = dequeue_signal(current, &ctx->sigmask, info);
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switch (ret) {
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case 0:
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if (!nonblock)
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break;
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ret = -EAGAIN;
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default:
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spin_unlock_irq(¤t->sighand->siglock);
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return ret;
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}
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add_wait_queue(¤t->sighand->signalfd_wqh, &wait);
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for (;;) {
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set_current_state(TASK_INTERRUPTIBLE);
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ret = dequeue_signal(current, &ctx->sigmask, info);
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if (ret != 0)
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break;
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if (signal_pending(current)) {
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ret = -ERESTARTSYS;
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break;
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}
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spin_unlock_irq(¤t->sighand->siglock);
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schedule();
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spin_lock_irq(¤t->sighand->siglock);
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}
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spin_unlock_irq(¤t->sighand->siglock);
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remove_wait_queue(¤t->sighand->signalfd_wqh, &wait);
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__set_current_state(TASK_RUNNING);
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return ret;
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}
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/*
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* Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
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* error code. The "count" parameter must be at least the size of a
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* "struct signalfd_siginfo".
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*/
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static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
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loff_t *ppos)
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{
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struct signalfd_ctx *ctx = file->private_data;
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struct signalfd_siginfo __user *siginfo;
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int nonblock = file->f_flags & O_NONBLOCK;
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ssize_t ret, total = 0;
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siginfo_t info;
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count /= sizeof(struct signalfd_siginfo);
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if (!count)
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return -EINVAL;
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siginfo = (struct signalfd_siginfo __user *) buf;
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do {
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ret = signalfd_dequeue(ctx, &info, nonblock);
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if (unlikely(ret <= 0))
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break;
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ret = signalfd_copyinfo(siginfo, &info);
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if (ret < 0)
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break;
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siginfo++;
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total += ret;
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nonblock = 1;
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} while (--count);
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return total ? total: ret;
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}
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#ifdef CONFIG_PROC_FS
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static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
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{
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struct signalfd_ctx *ctx = f->private_data;
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sigset_t sigmask;
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sigmask = ctx->sigmask;
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signotset(&sigmask);
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render_sigset_t(m, "sigmask:\t", &sigmask);
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}
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#endif
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static const struct file_operations signalfd_fops = {
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#ifdef CONFIG_PROC_FS
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.show_fdinfo = signalfd_show_fdinfo,
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#endif
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.release = signalfd_release,
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.poll = signalfd_poll,
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.read = signalfd_read,
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.llseek = noop_llseek,
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};
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SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
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size_t, sizemask, int, flags)
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{
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sigset_t sigmask;
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struct signalfd_ctx *ctx;
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/* Check the SFD_* constants for consistency. */
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BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
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BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
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if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
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return -EINVAL;
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if (sizemask != sizeof(sigset_t) ||
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copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
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return -EINVAL;
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sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
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signotset(&sigmask);
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if (ufd == -1) {
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ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
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if (!ctx)
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return -ENOMEM;
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ctx->sigmask = sigmask;
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/*
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* When we call this, the initialization must be complete, since
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* anon_inode_getfd() will install the fd.
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*/
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ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
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O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
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if (ufd < 0)
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kfree(ctx);
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} else {
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struct fd f = fdget(ufd);
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if (!f.file)
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return -EBADF;
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ctx = f.file->private_data;
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if (f.file->f_op != &signalfd_fops) {
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fdput(f);
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return -EINVAL;
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}
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spin_lock_irq(¤t->sighand->siglock);
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ctx->sigmask = sigmask;
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spin_unlock_irq(¤t->sighand->siglock);
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wake_up(¤t->sighand->signalfd_wqh);
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fdput(f);
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}
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return ufd;
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}
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SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
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size_t, sizemask)
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{
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return sys_signalfd4(ufd, user_mask, sizemask, 0);
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}
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#ifdef CONFIG_COMPAT
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COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
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const compat_sigset_t __user *,sigmask,
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compat_size_t, sigsetsize,
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int, flags)
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{
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compat_sigset_t ss32;
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sigset_t tmp;
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sigset_t __user *ksigmask;
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if (sigsetsize != sizeof(compat_sigset_t))
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return -EINVAL;
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if (copy_from_user(&ss32, sigmask, sizeof(ss32)))
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return -EFAULT;
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sigset_from_compat(&tmp, &ss32);
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ksigmask = compat_alloc_user_space(sizeof(sigset_t));
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if (copy_to_user(ksigmask, &tmp, sizeof(sigset_t)))
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return -EFAULT;
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return sys_signalfd4(ufd, ksigmask, sizeof(sigset_t), flags);
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}
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COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
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const compat_sigset_t __user *,sigmask,
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compat_size_t, sigsetsize)
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{
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return compat_sys_signalfd4(ufd, sigmask, sigsetsize, 0);
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}
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#endif
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