From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Herbert Xu <herbert@gondor.apana.org.au>,
Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: Fred Li <dracodingfly@gmail.com>,
aleksander.lobakin@intel.com, andrii@kernel.org,
ast@kernel.org, bpf@vger.kernel.org, daniel@iogearbox.net,
davem@davemloft.net, edumazet@google.com, haoluo@google.com,
hawk@kernel.org, john.fastabend@gmail.com, jolsa@kernel.org,
kpsingh@kernel.org, kuba@kernel.org,
linux-kernel@vger.kernel.org, linux@weissschuh.net,
martin.lau@linux.dev, mkhalfella@purestorage.com,
nbd@nbd.name, netdev@vger.kernel.org, pabeni@redhat.com,
sashal@kernel.org, sdf@google.com, song@kernel.org,
yonghong.song@linux.dev
Subject: Re: [PATCH] net: linearizing skb when downgrade gso_size
Date: Tue, 09 Jul 2024 17:29:59 -0400 [thread overview]
Message-ID: <668dabd7e7066_1ce27f29435@willemb.c.googlers.com.notmuch> (raw)
In-Reply-To: <Zo2auA2r/hkJWWcs@gondor.apana.org.au>
Herbert Xu wrote:
> On Tue, Jul 09, 2024 at 11:53:21AM -0400, Willem de Bruijn wrote:
> >
> > > + /* Due to header grow, MSS needs to be downgraded.
> > > + * There is BUG_ON When segment the frag_list with
> > > + * head_frag true so linearize skb after downgrade
> > > + * the MSS.
> > > + */
>
> This sounds completely wrong. You should never grow the TCP header
> by changing gso_size. What is the usage-scenario for this?
>
> Think about it, if a router forwards a TCP packet, and ends up
> growing its TCP header and then splits the packet into two, then
> this router is brain-dead.
This is an unfortunate feature, but already exists.
It decreases gso_size to account for tunnel headers.
For USO, we added BPF_F_ADJ_ROOM_FIXED_GSO to avoid this in better,
newer users.
next prev parent reply other threads:[~2024-07-09 21:30 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-26 6:55 [PATCH v2 2/2] test_bpf: Introduce an skb_segment test for frag_list whose head_frag=true and gso_size was mangled Fred Li
2024-06-26 6:55 ` [PATCH v2 1/2] net: Fix skb_segment when splitting gso_size mangled skb having linear-headed frag_list whose head_frag=true Fred Li
2024-07-02 9:23 ` Paolo Abeni
2024-07-03 12:21 ` Fred Li
2024-07-06 14:26 ` Willem de Bruijn
2024-07-08 14:31 ` [PATCH] net: linearizing skb when downgrade gso_size Fred Li
2024-07-09 15:53 ` Willem de Bruijn
2024-07-09 20:16 ` Herbert Xu
2024-07-09 21:29 ` Willem de Bruijn [this message]
2024-07-10 23:06 ` Herbert Xu
2024-07-12 8:17 ` Fred Li
2024-07-17 5:35 ` [PATCH v3] " Fred Li
2024-07-17 16:32 ` Willem de Bruijn
2024-07-18 7:42 ` Fred Li
2024-07-19 2:46 ` [PATCH v4] bpf: Fixed a segment issue " Fred Li
2024-07-19 18:22 ` Willem de Bruijn
2024-07-22 3:08 ` [PATCH bpf v5] bpf: Fixed " Fred Li
2024-07-22 16:29 ` Willem de Bruijn
2024-07-24 13:37 ` Fred Li
2024-07-25 10:09 ` Daniel Borkmann
2024-06-26 6:55 ` [PATCH v2 0/2] net: Fix BUG_ON for segment frag_list with mangled gso_size and head_frag is true Fred Li
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