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Date: Fri, 15 Dec 2017 15:59:46 -0800 From: Cong Wang <xiyou.wangcong@...il.com> To: Al Viro <viro@...iv.linux.org.uk> Cc: LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, stable <stable@...r.kernel.org>, gscrivan@...hat.com Subject: Re: [PATCH] exit: move exit_task_namespaces() after exit_task_work() On Thu, Dec 14, 2017 at 1:08 PM, Al Viro <viro@...iv.linux.org.uk> wrote: > On Thu, Dec 14, 2017 at 12:17:57PM -0800, Cong Wang wrote: >> syzbot reported we have a use-after-free when mqueue_evict_inode() >> is called on __cleanup_mnt() path, where the ipc ns is already >> freed by the previous exit_task_namespaces(). We can just move >> it after after exit_task_work() to avoid this use-after-free. > > What's to prevent somebody else holding a reference to the same > inode past the exit(2)? IOW, I don't believe that this is fixing > anything - in the best case, your patch papers over a specific > reproducer. You are right, I missed mq_clear_sbinfo(). And the offending commit is: commit 9c583773d036336176e9e50441890659bc4eeae8 Author: Giuseppe Scrivano <gscrivan@...hat.com> Date: Fri Dec 15 01:06:28 2017 +0000 ipc, mqueue: lazy call kern_mount_data in new namespaces kern_mount_data is a relatively expensive operation when creating a new IPC namespace, so delay the mount until its first usage when not creating the the global namespace. This is a net saving for new IPC namespaces that don't use mq_open(). In this case there won't be any kern_mount_data() cost at all. On my machine, the time for creating 1000 new IPC namespaces dropped from ~8s to ~2s. Link: http://lkml.kernel.org/r/20171206151422.9660-1-gscrivan@redhat.com Signed-off-by: Giuseppe Scrivano <gscrivan@...hat.com> Cc: Manfred Spraul <manfred@...orfullife.com> Cc: Davidlohr Bueso <dave@...olabs.net> Cc: Al Viro <viro@...iv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
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