[Precise][SRU] Yama: handle 32-bit userspace prctl

[Kees Cook]

BugLink: http://bugs.launchpad.net/bugs/1338883

commit 2e4930eb7c8fb20a39dfb5f8a8f80402710dcea8 upstream.

When running a 64-bit kernel and receiving prctls from a 32-bit
userspace, the "-1" used as an unsigned long will end up being
misdetected. The kernel is looking for 0xffffffffffffffff instead of
0xffffffff. Since prctl lacks a distinct compat interface, Yama needs
to handle this translation itself. As such, support either value as
meaning PR_SET_PTRACER_ANY, to avoid breaking the ABI for 64-bit.

Signed-off-by: Kees Cook <keescook at chromium.org>
Acked-by: John Johansen <john.johansen at canonical.com>
Cc: stable at vger.kernel.org
Signed-off-by: James Morris <james.l.morris at oracle.com>

[adjusted for Precise's Yama backport format/whitespace changes]
Signed-off-by: Kees Cook <kees at ubuntu.com>
---
 security/yama/yama_lsm.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index 30361cb..84bd07b 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -140,8 +140,7 @@ int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 		if (arg2 == 0) {
 			yama_ptracer_del(NULL, myself);
 			rc = 0;
-		}
-		else if (arg2 == PR_SET_PTRACER_ANY) {
+		} else if (arg2 == PR_SET_PTRACER_ANY || (int)arg2 == -1) {
 			rc = yama_ptracer_add(NULL, myself);
 		} else {
 			struct task_struct *tracer;
-- 
1.9.1


-- 
Kees Cook