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Message-ID: <66f3181c4fd22_3382d294b6@willemb.c.googlers.com.notmuch>
Date: Tue, 24 Sep 2024 15:50:52 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Felix Fietkau <nbd@....name>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>,
netdev@...r.kernel.org
Cc: davem@...emloft.net,
kuba@...nel.org,
edumazet@...gle.com,
pabeni@...hat.com,
stable@...r.kernel.org,
maze@...gle.com,
shiming.cheng@...iatek.com,
daniel@...earbox.net,
lena.wang@...iatek.com,
herbert@...dor.apana.org.au,
Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] gso: fix gso fraglist segmentation after pull from
frag_list
Felix Fietkau wrote:
> On 22.09.24 17:03, Willem de Bruijn wrote:
> > From: Willem de Bruijn <willemb@...gle.com>
> >
> > Detect gso fraglist skbs with corrupted geometry (see below) and
> > pass these to skb_segment instead of skb_segment_list, as the first
> > can segment them correctly.
> >
> > Valid SKB_GSO_FRAGLIST skbs
> > - consist of two or more segments
> > - the head_skb holds the protocol headers plus first gso_size
> > - one or more frag_list skbs hold exactly one segment
> > - all but the last must be gso_size
> >
> > Optional datapath hooks such as NAT and BPF (bpf_skb_pull_data) can
> > modify these skbs, breaking these invariants.
> >
> > In extreme cases they pull all data into skb linear. For UDP, this
> > causes a NULL ptr deref in __udpv4_gso_segment_list_csum at
> > udp_hdr(seg->next)->dest.
> >
> > Detect invalid geometry due to pull, by checking head_skb size.
> > Don't just drop, as this may blackhole a destination. Convert to be
> > able to pass to regular skb_segment.
> >
> > Link: https://lore.kernel.org/netdev/20240428142913.18666-1-shiming.cheng@mediatek.com/
> > Fixes: 3a1296a38d0c ("net: Support GRO/GSO fraglist chaining.")
> > Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> > Cc: stable@...r.kernel.org
> >
> > ---
> > diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> > index d842303587af..e457fa9143a6 100644
> > --- a/net/ipv4/udp_offload.c
> > +++ b/net/ipv4/udp_offload.c
> > @@ -296,8 +296,16 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
> > return NULL;
> > }
> >
> > - if (skb_shinfo(gso_skb)->gso_type & SKB_GSO_FRAGLIST)
> > - return __udp_gso_segment_list(gso_skb, features, is_ipv6);
> > + if (skb_shinfo(gso_skb)->gso_type & SKB_GSO_FRAGLIST) {
> > + /* Detect modified geometry and pass these to skb_segment. */
> > + if (skb_pagelen(gso_skb) - sizeof(*uh) == skb_shinfo(gso_skb)->gso_size)
> > + return __udp_gso_segment_list(gso_skb, features, is_ipv6);
> > +
> > + /* Setup csum, as fraglist skips this in udp4_gro_receive. */
> > + gso_skb->csum_start = skb_transport_header(gso_skb) - gso_skb->head;
> > + gso_skb->csum_offset = offsetof(struct udphdr, check);
> > + gso_skb->ip_summed = CHECKSUM_PARTIAL;
> > + }
>
> It seems to me that the TCP code would need something similar.
I think you're right, thanks.
Separate patch, as different Fixes, of course.
> Do you think the same approach would work there as well?
tcp4_gro_complete seems to mirror udp4_gro_receive in returning early
before setting up checksum offload. So likely yes.
The script I shared to reproduce for UDP can hopefully be reused
easily to also generate these packets with TCP.
> Thanks,
>
> - Felix
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