linux-kernel - [PATCH] posix-timers: fix stack info leak in timer

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Date:	Sat,  4 Oct 2014 23:06:39 +0200
From:	Mathias Krause <minipli@...glemail.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org,
	Mathias Krause <minipli@...glemail.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Brad Spengler <spender@...ecurity.net>,
	PaX Team <pageexec@...email.hu>
Subject: [PATCH] posix-timers: fix stack info leak in timer_create()

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.

Initialize sigev_value with 0 to plug the stack info leak.

Found in the PaX patch, written by the PaX Team.

Fixes: 5a9fa7307285 ("posix-timers: kill ->it_sigev_signo and...")
Signed-off-by: Mathias Krause <minipli@...glemail.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Brad Spengler <spender@...ecurity.net>
Cc: PaX Team <pageexec@...email.hu>
Cc: <stable@...r.kernel.org>	# v2.6.28+
---
 kernel/time/posix-timers.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index 42b463ad90f2..31ea01f42e1f 100644
--- 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;
-- 
1.7.10.4

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