signalfd: fix information leak in signalfd_copyinfo

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>

diff --git a/fs/signalfd.c b/fs/signalfd.c
index 7e412ad748363489baad12cbb644b8074d78cfeb..270221fcef42cc42fcfdbc098b587b571be65a12 100644 (file)
--- 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