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

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Message-ID: <20190326041509.GZ2217@ZenIV.linux.org.uk>
Date:   Tue, 26 Mar 2019 04:15:10 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Mark Fasheh <mark@...heh.com>
Cc:     Dave Chinner <david@...morbit.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        syzbot <syzbot+7a8ba368b47fdefca61e@...kaller.appspotmail.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Jan Kara <jack@...e.cz>, Jaegeuk Kim <jaegeuk@...nel.org>,
        Joel Becker <jlbec@...lplan.org>
Subject: Re: KASAN: use-after-free Read in path_lookupat

On Mon, Mar 25, 2019 at 08:18:25PM -0700, Mark Fasheh wrote:

> Hey Al,
> 
> It's been a while since I've looked at that bit of code but it looks like
> Ocfs2 is syncing the inode to disk and disposing of it's memory
> representation (which would include the cluster locks held) so that other
> nodes get a chance to delete the potentially orphaned inode. In Ocfs2 we
> won't delete an inode if it exists in another nodes cache.

Wait a sec - what's the reason for forcing that write_inode_now(); why
doesn't the normal mechanism work?  I'm afraid I still don't get it -
we do wait for writeback in evict_inode(), or the local filesystems
wouldn't work.