linux-kernel - [PATCH 3.16.y-ckt 128/130] signalfd: fix information leak in signalfd

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Message-Id: <1441372118-5933-129-git-send-email-luis.henriques@canonical.com>
Date:	Fri,  4 Sep 2015 14:08:36 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Amanieu d'Antras <amanieu@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 128/130] signalfd: fix information leak in signalfd_copyinfo

3.16.7-ckt17 -stable review patch.  If anyone has any objections, please let me know.

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

From: Amanieu d'Antras <amanieu@...il.com>

commit 3ead7c52bdb0ab44f4bb1feed505a8323cc12ba7 upstream.

This function may copy the si_addr_lsb field to user mode when it hasn't
been initialized, which can leak kernel stack data to user mode.

Just checking the value of si_code is insufficient because the same
si_code value is shared between multiple signals.  This is solved by
checking the value of si_signo in addition to si_code.

Signed-off-by: Amanieu d'Antras <amanieu@...il.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 fs/signalfd.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/signalfd.c b/fs/signalfd.c
index 424b7b65321f..148f8e7af882 100644
--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -121,8 +121,9 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
 		 * Other callers might not initialize the si_lsb field,
 		 * so check explicitly for the right codes here.
 		 */
-		if (kinfo->si_code == BUS_MCEERR_AR ||
-		    kinfo->si_code == BUS_MCEERR_AO)
+		if (kinfo->si_signo == SIGBUS &&
+		    (kinfo->si_code == BUS_MCEERR_AR ||
+		     kinfo->si_code == BUS_MCEERR_AO))
 			err |= __put_user((short) kinfo->si_addr_lsb,
 					  &uinfo->ssi_addr_lsb);
 #endif
--
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