linux-kernel - Re: [syzbot] WARNING in mntput_no

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Date:   Sun, 4 Apr 2021 20:17:21 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        syzbot <syzbot+c88a7030da47945a3cc3@...kaller.appspotmail.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, io-uring@...r.kernel.org
Subject: Re: [syzbot] WARNING in mntput_no_expire (2)

On Sun, Apr 04, 2021 at 06:50:10PM +0000, Al Viro wrote:

> > Yeah, I have at least namei.o
> > 
> > https://drive.google.com/file/d/1AvO1St0YltIrA86DXjp1Xg3ojtS9owGh/view?usp=sharing
> 
> *grumble*
> 
> Is it reproducible without KASAN?  Would be much easier to follow the produced
> asm...

	Looks like inode_permission(_, NULL, _) from may_lookup(nd).  I.e.
nd->inode == NULL.

	Mind slapping BUG_ON(!nd->inode) right before may_lookup() call in
link_path_walk() and trying to reproduce that oops?