Felix Fietkau wrote:
On 22.09.24 17:03, Willem de Bruijn wrote:
From: Willem de Bruijn willemb@google.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... Fixes: 3a1296a38d0c ("net: Support GRO/GSO fraglist chaining.") Signed-off-by: Willem de Bruijn willemb@google.com Cc: stable@vger.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