linux-kernel - Re: fscache corruption in Linux 5.17?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Yl8pRVSW9y1o6MBV@rabbit.intern.cm-ag>
Date:   Tue, 19 Apr 2022 23:27:33 +0200
From:   Max Kellermann <mk@...all.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Max Kellermann <mk@...all.com>, linux-cachefs@...hat.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: fscache corruption in Linux 5.17?

On 2022/04/19 18:42, David Howells <dhowells@...hat.com> wrote:
> Could the file have been modified by a third party?  If you're using NFS3
> there's a problem if two clients can modify a file at the same time.  The
> second write can mask the first write and the client has no way to detect it.
> The problem is inherent to the protocol design.  The NFS2 and NFS3 protocols
> don't support anything better than {ctime,mtime,filesize} - the change
> attribute only becomes available with NFS4.

I tried to write a script to stress-test writing and reading, but
found no clue so far.  I'll continue that tomorrow.

My latest theory is that this is a race condition; what if one process
writes to the file, which invalidates the cache; then, in the middle
of invalidating the local cache and sending the write to the NFS
server, another process (on the same server) reads the file; what
modification time and what data will it see?  What if the cache gets
filled with old data, while new data to-be-written is still in flight?

Max