Felix Fietkau wrote: > On 22.09.24 17:03, Willem de Bruijn wrote: > > From: Willem de Bruijn <willemb@xxxxxxxxxx> > > > > 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@xxxxxxxxxxxx/ > > Fixes: 3a1296a38d0c ("net: Support GRO/GSO fraglist chaining.") > > Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx> > > Cc: stable@xxxxxxxxxxxxxxx > > > > --- > > 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; > > I also noticed this uh->check update done by udp4_gro_complete only in > case of non-fraglist GRO: > > if (uh->check) > uh->check = ~udp_v4_check(skb->len - nhoff, iph->saddr, > iph->daddr, 0); > > I didn't see any equivalent in your patch. Is it missing or left out > intentionally? Thanks. That was not intentional. I think you're right. Am a bit concerned that all this testing did not catch it. Perhaps because CHECKSUM_PARTIAL looped to ingress on the same machine is simply interpreted as CHECKSUM_UNNECESSARY. Need to look into that. If respinning this, I should also change the Fixes to Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.") Analogous to the eventual TCP fix to Fixes: bee88cd5bd83 ("net: add support for segmenting TCP fraglist GSO packets")
