Messages in this thread | | | Date | Sun, 5 Oct 2014 23:06:14 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] posix-timers: fix stack info leak in timer_create() |
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On 10/04, Mathias Krause wrote: > > If userland creates a timer without specifying a sigevent info, we'll > create one ourself, using a stack local variable. Particularly will we > use the timer ID as sival_int. But as sigev_value is a union containing > a pointer and an int, that assignment will only partially initialize > sigev_value on systems where the size of a pointer is bigger than the > size of an int. On such systems we'll copy the uninitialized stack bytes > from the timer_create() call to userland when the timer actually fires > and we're going to deliver the signal.
So we have a minor information leak,
> Cc: <stable@vger.kernel.org> # v2.6.28+
not sure this is -stable material but I won't really argue.
> --- a/kernel/time/posix-timers.c > +++ b/kernel/time/posix-timers.c > @@ -636,6 +636,7 @@ SYSCALL_DEFINE3(timer_create, const clockid_t, which_clock, > goto out; > } > } else { > + memset(&event.sigev_value, 0, sizeof(event.sigev_value)); > event.sigev_notify = SIGEV_SIGNAL; > event.sigev_signo = SIGALRM; > event.sigev_value.sival_int = new_timer->it_id;
How about
- event.sigev_value.sival_int = new_timer->it_id; + event.sigev_value = (sigval_t) { .sival_int = new_timer_id };
?
(btw, new_timer->sigq->info.si_tid initialization can use new_timer_id too)
this makes the initialization more explicit and can help gcc to optimize this assignment although this is minor.
In any case this all looks confusing to me. sys_timer_create() does
new_timer->sigq->info.si_value = event.sigev_value; new_timer->sigq->info.si_tid = new_timer->it_id;
later, this writes to the differents members (_rt and _timer) in the same union. But the comment in struct siginfo says that we should use _timer. And copy_siginfo_to_user() reports si_tid and si_ptr, this again reads _timer and _rt. This should actually work, _sigval should have the same offset in both struct's, still it looks confusing imho. Perhaps we should change
#define si_value _sifields._rt._sigval #define si_int _sifields._rt._sigval.sival_int #define si_ptr _sifields._rt._sigval.sival_ptr
to use _timer instead. Nevermind, this is off-topic.
Oleg.
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