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Subject[PATCH 3.16.y-ckt 128/130] signalfd: fix information leak in signalfd_copyinfo
Date
3.16.7-ckt17 -stable review patch.  If anyone has any objections, please let me know.

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

From: Amanieu d'Antras <amanieu@gmail.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@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.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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