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signals: don't abuse __flush_signals() in selinux_bprm_committed_creds()

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selinux_bprm_committed_creds()->__flush_signals() is not right, we
shouldn't clear TIF_SIGPENDING unconditionally. There can be other
reasons for signal_pending(): freezing(), JOBCTL_PENDING_MASK, and
potentially more.

Also change this code to check fatal_signal_pending() rather than
SIGNAL_GROUP_EXIT, it looks a bit better.

Now we can kill __flush_signals() before it finds another buggy user.

Note: this code looks racy, we can flush a signal which was sent after
the task SID has been updated.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>
This commit is contained in:
Oleg Nesterov 2015-06-04 16:22:16 -04:00 committed by Paul Moore
parent cded3fffbe
commit 9e7c8f8c62
3 changed files with 8 additions and 12 deletions
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1
include/linux/sched.h
View File

@ -2373,7 +2373,6 @@ extern void sched_dead(struct task_struct *p);
extern void proc_caches_init(void);
extern void flush_signals(struct task_struct *);
extern void __flush_signals(struct task_struct *);
extern void ignore_signals(struct task_struct *);
extern void flush_signal_handlers(struct task_struct *, int force_default);
extern int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info);

13
kernel/signal.c
View File

@ -414,21 +414,16 @@ void flush_sigqueue(struct sigpending *queue)
}
/*
* Flush all pending signals for a task.
* Flush all pending signals for this kthread.
*/
void __flush_signals(struct task_struct *t)
{
clear_tsk_thread_flag(t, TIF_SIGPENDING);
flush_sigqueue(&t->pending);
flush_sigqueue(&t->signal->shared_pending);
}
void flush_signals(struct task_struct *t)
{
unsigned long flags;
spin_lock_irqsave(&t->sighand->siglock, flags);
__flush_signals(t);
clear_tsk_thread_flag(t, TIF_SIGPENDING);
flush_sigqueue(&t->pending);
flush_sigqueue(&t->signal->shared_pending);
spin_unlock_irqrestore(&t->sighand->siglock, flags);
}

6
security/selinux/hooks.c
View File

@ -2416,10 +2416,12 @@ static void selinux_bprm_committed_creds(struct linux_binprm *bprm)
for (i = 0; i < 3; i++)
do_setitimer(i, &itimer, NULL);
spin_lock_irq(&current->sighand->siglock);
if (!(current->signal->flags & SIGNAL_GROUP_EXIT)) {
__flush_signals(current);
if (!fatal_signal_pending(current)) {
flush_sigqueue(&current->pending);
flush_sigqueue(&current->signal->shared_pending);
flush_signal_handlers(current, 1);
sigemptyset(&current->blocked);
recalc_sigpending();
}
spin_unlock_irq(&current->sighand->siglock);
}