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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat, 9 Nov 2019 08:55:38 -0800
Message-ID: <CAHk-=wg9e5PDG-y-j6uryc0RCbfZ36yB0a8qBb2hCWNrH4r_3g@mail.gmail.com>
Subject: Re: [PATCH][RFC] race in exportfs_decode_fh()
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     "J. Bruce Fields" <bfields@fieldses.org>,
        Ritesh Harjani <riteshh@linux.ibm.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        wugyuan@cn.ibm.com, Jeff Layton <jlayton@kernel.org>,
        hsiangkao@aol.com, Jan Kara <jack@suse.cz>,
        Christoph Hellwig <hch@lst.de>
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On Fri, Nov 8, 2019 at 7:13 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> We have derived the parent from fhandle, we have a disconnected dentry for child,
> we go look for the name.  We even find it.  Now, we want to look it up.  And
> some bastard goes and unlinks it, just as we are trying to lock the parent.
> We do a lookup, and get a negative dentry.  Then we unlock the parent... and
> some other bastard does e.g. mkdir with the same name.  OK, nresult->d_inode
> is not NULL (anymore).  It has fuck-all to do with the original fhandle
> (different inumber, etc.) but we happily accept it.

No arguments with your patch, although I doubt that this case has
actually ever happened in practice ;)

              Linus