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From: Kees Cook <keescook@chromium.org>
To: James Morris <jmorris@namei.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-security-module <linux-security-module@vger.kernel.org>,
	syzbot <syzbot+a9ac39bf55329e206219@syzkaller.appspotmail.com>,
	syzkaller-bugs@googlegroups.com
Subject: [PATCH] Yama: Check for pid death before checking ancestry
Date: Wed, 16 Jan 2019 10:31:09 -0800	[thread overview]
Message-ID: <20190116183109.GA21722@beast> (raw)

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>
---
James, can you please send this to Linus in your -fixes tree?
---
 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;
-- 
2.17.1


-- 
Kees Cook

             reply	other threads:[~2019-01-16 18:31 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-16 18:31 Kees Cook [this message]
2019-01-16 20:02 ` James Morris
2019-01-16 20:02   ` James Morris

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