From f6581f5b55141a95657ef5742cf6a6bfa20a109f Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 29 May 2019 13:31:57 +0200 Subject: ptrace: restore smp_rmb() in __ptrace_may_access() Restore the read memory barrier in __ptrace_may_access() that was deleted a couple years ago. Also add comments on this barrier and the one it pairs with to explain why they're there (as far as I understand). Fixes: bfedb589252c ("mm: Add a user_ns owner to mm_struct and fix ptrace permission checks") Cc: stable@vger.kernel.org Acked-by: Kees Cook Acked-by: Oleg Nesterov Signed-off-by: Jann Horn Signed-off-by: Eric W. Biederman --- kernel/cred.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'kernel/cred.c') diff --git a/kernel/cred.c b/kernel/cred.c index 45d77284aed0..07e069d00696 100644 --- a/kernel/cred.c +++ b/kernel/cred.c @@ -450,6 +450,15 @@ int commit_creds(struct cred *new) if (task->mm) set_dumpable(task->mm, suid_dumpable); task->pdeath_signal = 0; + /* + * If a task drops privileges and becomes nondumpable, + * the dumpability change must become visible before + * the credential change; otherwise, a __ptrace_may_access() + * racing with this change may be able to attach to a task it + * shouldn't be able to attach to (as if the task had dropped + * privileges without becoming nondumpable). + * Pairs with a read barrier in __ptrace_may_access(). + */ smp_wmb(); } -- cgit v1.2.3-59-g8ed1b