Yama: handle 32-bit userspace prctl

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 <[email protected]>
Acked-by: John Johansen <[email protected]>
Cc: [email protected]
Signed-off-by: James Morris <[email protected]>

security/yama/yama_lsm.c

@@ -143,7 +143,7 @@ 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;