linux-kernel - Re: KASAN: use-after-free Read in mnt_warn_timestamp

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Date:   Thu, 17 Oct 2019 02:58:53 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     syzbot <syzbot+76a43f2b4d34cfc53548@...kaller.appspotmail.com>,
        akpm@...l.org, deepa.kernel@...il.com, hch@...radead.org,
        jlayton@...nel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, lkundrak@...sk,
        syzkaller-bugs@...glegroups.com, tklauser@...rscht.ch,
        trond.myklebust@....uio.no
Subject: Re: KASAN: use-after-free Read in mnt_warn_timestamp_expiry

On Wed, Oct 16, 2019 at 06:47:55PM -0700, Eric Biggers wrote:
> On Wed, Oct 16, 2019 at 06:42:11PM -0700, syzbot wrote:
> > ==================================================================
> > BUG: KASAN: use-after-free in mnt_warn_timestamp_expiry+0x4a/0x250
> > fs/namespace.c:2471
> > Read of size 8 at addr ffff888099937328 by task syz-executor.1/18510
> > 
> 
> Looks like a duplicate of this:
> 
> #syz dup: KASAN: use-after-free Read in do_mount
> 
> See the existing thread and proposed fix here:
> https://lkml.kernel.org/linux-fsdevel/000000000000805e5505945a234b@google.com/T/#u

FWIW, I'd go with your "move mnt_warn_timestamp_expiry() up".  However,
I'd probably turn the message into something like
	foofs filesystem getting mounted at /mnt/barf supports...
And s/mounted/reconfigured/ if mnt_has_parent(mnt) is already true.

Objections?

Al, currently experiencing the joy of being ears-deep in 5 different shitpiles
simultaneously...