From 9474f4e7cd71a633fa1ef93b7daefd44bbdfd482 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Wed, 16 Jan 2019 10:31:09 -0800
Subject: [PATCH] Yama: Check for pid death before checking ancestry
Git-commit: 9474f4e7cd71a633fa1ef93b7daefd44bbdfd482
Patch-mainline: v5.0-rc3
References: bsc#1051510
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: syzbot+a9ac39bf55329e206219@syzkaller.appspotmail.com
Fixes: 2d514487faf1 ("security: Yama LSM")
Cc: stable@vger.kernel.org
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.morris@microsoft.com>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
security/yama/yama_lsm.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index ffda91a4a1aa..02514fe558b4 100644
--- 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;
--
2.16.4