netdev - Re: [PATCH net] tcp: Always cleanup skb before sending

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]

Date:   Wed, 1 Nov 2017 14:32:53 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Christoph Paasch <cpaasch@...le.com>
Cc:     David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] tcp: Always cleanup skb before sending

On Wed, Nov 1, 2017 at 2:10 PM, Christoph Paasch <cpaasch@...le.com> wrote:
> Since commit 971f10eca186 ("tcp: better TCP_SKB_CB layout to reduce cache
> line misses") IPCB/IP6CB is no more at the beginning of the tcp_skb_cb.
> This means that on the output path, we need to make sure that it has
> been correctly initialized to 0, as is done in tcp_transmit_skb.
>
> However, when going through the other code-path in TCP that can send an
> skb (e.g., through tcp_v6_send_synack), we end up in a situation where
> IP6CB has some of its fields set to unexpected values. Depending on the
> layout of tcp_skb_cb across the different kernel-versions this can be
> lastopt, flags,...

Or not use tcp_init_nondata_skb() on non fast clones, since it adds
unnecessary writes and clears.

tcp_make_synack() really has no business using tcp_init_nondata_skb()
and could simply set th->seq = htonl(tcp_rsk(req)->snt_isn);