From b955a2c75675102b8270fd06c6c2730913994ce7 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 16 Jan 2019 10:31:09 -0800 Subject: [PATCH] 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: syzbot+a9ac39bf55329e206219@syzkaller.appspotmail.com Fixes: 2d514487faf1 ("security: Yama LSM") Cc: stable@vger.kernel.org Suggested-by: Oleg Nesterov Signed-off-by: Kees Cook Signed-off-by: James Morris Signed-off-by: Greg Kroah-Hartman --- 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 ffda91a..02514fe 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; -- 2.7.4