4.20-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kees Cook keescook@chromium.org
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 oleg@redhat.com Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: James Morris james.morris@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- security/yama/yama_lsm.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/security/yama/yama_lsm.c +++ b/security/yama/yama_lsm.c @@ -368,7 +368,9 @@ static int yama_ptrace_access_check(stru 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;