[PATCH 4.1 79/84] signalfd: fix information leak in signalfd_copyinfo

From: Greg Kroah-Hartman
Date: Fri Aug 14 2015 - 13:44:42 EST

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


From: Amanieu d'Antras <amanieu@xxxxxxxxx>

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@xxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

fs/signalfd.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -121,8 +121,9 @@ static int signalfd_copyinfo(struct sign
* 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,

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