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;
+ }
It seems to me that the TCP code would need something similar. Do you
think the same approach would work there as well?
Thanks,
- Felix
