signal: fix information leak in copy_siginfo_to_user

This function may copy the si_addr_lsb, si_lower and si_upper fields to
user mode when they haven'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>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index 81fd38f4fbaaf1b9ef340aee5d1e2d8de9fa7d60..948f0ad2de231b5e3f5efa62e204162cadf26503 100644 (file)
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c
@@ -168,7 +168,8 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
                 * Other callers might not initialize the si_lsb field,
                 * so check explicitely for the right codes here.
                 */
-               if (from->si_code == BUS_MCEERR_AR || from->si_code == BUS_MCEERR_AO)
+               if (from->si_signo == SIGBUS &&
+                   (from->si_code == BUS_MCEERR_AR || from->si_code == BUS_MCEERR_AO))
                        err |= __put_user(from->si_addr_lsb, &to->si_addr_lsb);
 #endif
                break;

diff --git a/kernel/signal.c b/kernel/signal.c
index 00524cf6c41206db2da7b75ec66ceb712db26810..0f6bbbe77b46c092d0de31e0c9eec8a0f17e6791 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2748,12 +2748,15 @@ int copy_siginfo_to_user(siginfo_t __user *to, const siginfo_t *from)
                 * Other callers might not initialize the si_lsb field,
                 * so check explicitly for the right codes here.
                 */
-               if (from->si_code == BUS_MCEERR_AR || from->si_code == BUS_MCEERR_AO)
+               if (from->si_signo == SIGBUS &&
+                   (from->si_code == BUS_MCEERR_AR || from->si_code == BUS_MCEERR_AO))
                        err |= __put_user(from->si_addr_lsb, &to->si_addr_lsb);
 #endif
 #ifdef SEGV_BNDERR
-               err |= __put_user(from->si_lower, &to->si_lower);
-               err |= __put_user(from->si_upper, &to->si_upper);
+               if (from->si_signo == SIGSEGV && from->si_code == SEGV_BNDERR) {
+                       err |= __put_user(from->si_lower, &to->si_lower);
+                       err |= __put_user(from->si_upper, &to->si_upper);
+               }
 #endif
                break;
        case __SI_CHLD: