From 26e9781fbdae8ed52017abfd11d034022892ba41 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 BugLink: https://bugs.launchpad.net/bugs/1837477 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 Signed-off-by: Kamal Mostafa Signed-off-by: Khalid Elmously --- 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 8298e094f4f7..7d5541c6a225 100644 --- a/security/yama/yama_lsm.c +++ b/security/yama/yama_lsm.c @@ -373,7 +373,9 @@ 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; -- 2.39.2