netdev - Re: [PATCH net v2] tcp: fix page frag corruption on page fault

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Date:   Fri, 26 Nov 2021 16:26:27 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, Steffen Froemer <sfroemer@...hat.com>
Subject: Re: [PATCH net v2] tcp: fix page frag corruption on page fault

On Fri, Nov 26, 2021 at 10:35 AM Paolo Abeni <pabeni@...hat.com> wrote:
>
> Steffen reported a TCP stream corruption for HTTP requests
> served by the apache web-server using a cifs mount-point
> and memory mapping the relevant file.
>
> The root cause is quite similar to the one addressed by
> commit 20eb4f29b602 ("net: fix sk_page_frag() recursion from
> memory reclaim"). Here the nested access to the task page frag
> is caused by a page fault on the (mmapped) user-space memory
> buffer coming from the cifs file.
>
> The page fault handler performs an smb transaction on a different
> socket, inside the same process context. Since sk->sk_allaction
> for such socket does not prevent the usage for the task_frag,
> the nested allocation modify "under the hood" the page frag
> in use by the outer sendmsg call, corrupting the stream.
>

> v1 -> v2:
>  - use a stricted sk_page_frag() check instead of reordering the
>    code (Eric)
>
> Reported-by: Steffen Froemer <sfroemer@...hat.com>
> Fixes: 5640f7685831 ("net: use a per task frag allocator")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---

SGTM, thanks !

Reviewed-by: Eric Dumazet <edumazet@...gle.com>