linux-kernel - Re: WARNING in kmem_cache

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Message-ID: <20180408055900.GH30522@ZenIV.linux.org.uk>
Date:   Sun, 8 Apr 2018 06:59:13 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+75397ee3df5c70164154@...kaller.appspotmail.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: WARNING in kmem_cache_free

On Fri, Apr 06, 2018 at 03:33:36PM +0200, Dmitry Vyukov wrote:

> Interesting type of bug, I think we see this for the first time.
> 
> Al, do you see how this can happen?

putname() on something that hasn't come from getname().  Short
of reproducer, I don't see what can be done - it can be any
kind of memory corruption.  We have
        return filename_lookup(dfd, getname_flags(name, flags, empty),
                               flags, path, NULL);
with filename_lookup() hitting
        putname(name);
        return retval;
on the way out (and seeing refcount 1, at that, so it hasn't ended
up in audit context).  And object it's trying to free is not something
getname_flags() has allocated.