Yama: Check for pid death before checking ancestry

commit 9474f4e7cd71a633fa1ef93b7daefd44bbdfd482 upstream. It's possible that a pid has died before we take the rcu lock, in which case we can't walk the ancestry list as it may be detached. Instead, check for death first before doing the walk. Reported-by: [email protected] Fixes: 2d51448 ("security: Yama LSM") Cc: [email protected] Suggested-by: Oleg Nesterov <[email protected]> Signed-off-by: Kees Cook <[email protected]> Signed-off-by: James Morris <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
BootleggersROM-Devices · Jan 22, 2019 · b955a2c · b955a2c
1 parent 01634ac
commit b955a2c
Showing 1 changed file with 3 additions and 1 deletion.
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
@@ -368,7 +368,9 @@ static int yama_ptrace_access_check(struct task_struct *child,
 			break;
 		case YAMA_SCOPE_RELATIONAL:
 			rcu_read_lock();
-			if (!task_is_descendant(current, child) &&
+			if (!pid_alive(child))
+				rc = -EPERM;
+			if (!rc && !task_is_descendant(current, child) &&
 			    !ptracer_exception_found(current, child) &&
 			    !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
 				rc = -EPERM;