linux-kernel - [ 46/48] posix-timers: Fix stack info leak in timer

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Date:	Fri, 15 May 2015 10:06:16 +0200
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Mathias Krause <minipli@...glemail.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Brad Spengler <spender@...ecurity.net>,
	PaX Team <pageexec@...email.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ben Hutchings <ben@...adent.org.uk>, Willy Tarreau <w@....eu>
Subject: [ 46/48] posix-timers: Fix stack info leak in timer_create()

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Mathias Krause <minipli@...glemail.com>

commit 6891c4509c792209c44ced55a60f13954cb50ef4 upstream.

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>
Link: http://lkml.kernel.org/r/1412456799-32339-1-git-send-email-minipli@googlemail.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
(cherry picked from commit 3cd3a349aa3519b88d29845c0bc36bcbae158e93)

Signed-off-by: Willy Tarreau <w@....eu>
---
 kernel/posix-timers.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 5e76d22..f2335e8 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -578,6 +578,7 @@ 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;
-- 
1.7.12.2.21.g234cd45.dirty



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