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fix race between exit_itimers() and /proc/pid/timers

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commit d5b36a4dbd upstream.

As Chris explains, the comment above exit_itimers() is not correct,
we can race with proc_timers_seq_ops. Change exit_itimers() to clear
signal->posix_timers with ->siglock held.

Cc: <stable@vger.kernel.org>
Reported-by: chris@accessvector.net
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Oleg Nesterov 2022-07-11 18:16:25 +02:00 • committed by Justin Hammond
parent 9fbc46b832
commit 51fc55e41c
4 changed files with 17 additions and 8 deletions
Download patch file Download diff file Expand all files Collapse all files

2
fs/exec.c
View file

@ -1298,7 +1298,7 @@ int begin_new_exec(struct linux_binprm * bprm)
bprm->mm = NULL; bprm->mm = NULL;
#ifdef CONFIG_POSIX_TIMERS #ifdef CONFIG_POSIX_TIMERS
exit_itimers(me->signal); exit_itimers(me);
flush_itimer_signals(); flush_itimer_signals();
#endif #endif

2
include/linux/sched/task.h
View file

@ -81,7 +81,7 @@ static inline void exit_thread(struct task_struct *tsk)
extern void do_group_exit(int); extern void do_group_exit(int);
extern void exit_files(struct task_struct *); extern void exit_files(struct task_struct *);
extern void exit_itimers(struct signal_struct *); extern void exit_itimers(struct task_struct *);
extern pid_t kernel_clone(struct kernel_clone_args *kargs); extern pid_t kernel_clone(struct kernel_clone_args *kargs);
struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node); struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node);

2
kernel/exit.c
View file

@ -796,7 +796,7 @@ void __noreturn do_exit(long code)
#ifdef CONFIG_POSIX_TIMERS #ifdef CONFIG_POSIX_TIMERS
hrtimer_cancel(&tsk->signal->real_timer); hrtimer_cancel(&tsk->signal->real_timer);
exit_itimers(tsk->signal); exit_itimers(tsk);
#endif #endif
if (tsk->mm) if (tsk->mm)
setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm); setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm);

19
kernel/time/posix-timers.c
View file

@ -1051,15 +1051,24 @@ retry_delete:
} }
/* /*
* This is called by do_exit or de_thread, only when there are no more * This is called by do_exit or de_thread, only when nobody else can
* references to the shared signal_struct. * modify the signal->posix_timers list. Yet we need sighand->siglock
* to prevent the race with /proc/pid/timers.
*/ */
void exit_itimers(struct signal_struct *sig) void exit_itimers(struct task_struct *tsk)
{ {
struct list_head timers;
struct k_itimer *tmr; struct k_itimer *tmr;
while (!list_empty(&sig->posix_timers)) { if (list_empty(&tsk->signal->posix_timers))
tmr = list_entry(sig->posix_timers.next, struct k_itimer, list); return;
spin_lock_irq(&tsk->sighand->siglock);
list_replace_init(&tsk->signal->posix_timers, &timers);
spin_unlock_irq(&tsk->sighand->siglock);
while (!list_empty(&timers)) {
tmr = list_first_entry(&timers, struct k_itimer, list);
itimer_delete(tmr); itimer_delete(tmr);
} }
} }