kernel: fix crashes after linearizing fraglist GSO skbs

This fixes some corner cases triggered by enabling fraglist GRO, where some
protocols may accidentally or intentionally linearize fraglist skbs.
Previously, these skbs became unusable and segmenting them led to crashes.
With this patch, they are properly handled by passing them to skb_segment
instead of skb_segment_list.

Signed-off-by: Felix Fietkau <[email protected]>

target/linux/generic/pending-6.6/684-gso-fix-gso-fraglist-segmentation-after-pull-from-fr.patch

@@ -0,0 +1,53 @@
+From: Willem de Bruijn <[email protected]>
+Date: Sun, 22 Sep 2024 11:03:45 -0400
+Subject: [PATCH] gso: fix gso fraglist segmentation after pull from
+ frag_list
+
+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/[email protected]/
+Fixes: 3a1296a38d0c ("net: Support GRO/GSO fraglist chaining.")
+Signed-off-by: Willem de Bruijn <[email protected]>
+Cc: [email protected]
+---
+
+--- a/net/ipv4/udp_offload.c
++++ b/net/ipv4/udp_offload.c
+@@ -296,8 +296,16 @@ struct sk_buff *__udp_gso_segment(struct
+ 		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;
++	}
+ 
+ 	skb_pull(gso_skb, sizeof(*uh));
+ 

target/linux/generic/pending-6.6/685-net-gso-fix-tcp-fraglist-segmentation-after-pull-fro.patch

@@ -0,0 +1,74 @@
+From: Felix Fietkau <[email protected]>
+Date: Thu, 26 Sep 2024 10:41:30 +0200
+Subject: [PATCH] net: gso: fix tcp fraglist segmentation after pull from
+ frag_list
+
+Detect tcp 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 TCP, this
+causes a NULL ptr deref in __tcpv4_gso_segment_list_csum at
+tcp_hdr(seg->next).
+
+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.
+
+Approach and description based on a patch by Willem de Bruijn.
+
+Link: https://lore.kernel.org/netdev/[email protected]/
+Link: https://lore.kernel.org/netdev/[email protected]/
+Fixes: bee88cd5bd83 ("net: add support for segmenting TCP fraglist GSO packets")
+Cc: [email protected]
+Cc: Willem de Bruijn <[email protected]>
+Signed-off-by: Felix Fietkau <[email protected]>
+---
+
+--- a/net/ipv4/tcp_offload.c
++++ b/net/ipv4/tcp_offload.c
+@@ -101,8 +101,14 @@ static struct sk_buff *tcp4_gso_segment(
+ 	if (!pskb_may_pull(skb, sizeof(struct tcphdr)))
+ 		return ERR_PTR(-EINVAL);
+ 
+-	if (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST)
+-		return __tcp4_gso_segment_list(skb, features);
++	if (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST) {
++		struct tcphdr *th = tcp_hdr(skb);
++
++		if (skb_pagelen(skb) - th->doff * 4 == skb_shinfo(skb)->gso_size)
++			return __tcp4_gso_segment_list(skb, features);
++
++		skb->ip_summed = CHECKSUM_NONE;
++	}
+ 
+ 	if (unlikely(skb->ip_summed != CHECKSUM_PARTIAL)) {
+ 		const struct iphdr *iph = ip_hdr(skb);
+--- a/net/ipv6/tcpv6_offload.c
++++ b/net/ipv6/tcpv6_offload.c
+@@ -158,8 +158,14 @@ static struct sk_buff *tcp6_gso_segment(
+ 	if (!pskb_may_pull(skb, sizeof(*th)))
+ 		return ERR_PTR(-EINVAL);
+ 
+-	if (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST)
+-		return __tcp6_gso_segment_list(skb, features);
++	if (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST) {
++		struct tcphdr *th = tcp_hdr(skb);
++
++		if (skb_pagelen(skb) - th->doff * 4 == skb_shinfo(skb)->gso_size)
++			return __tcp6_gso_segment_list(skb, features);
++
++		skb->ip_summed = CHECKSUM_NONE;
++	}
+ 
+ 	if (unlikely(skb->ip_summed != CHECKSUM_PARTIAL)) {
+ 		const struct ipv6hdr *ipv6h = ipv6_hdr(skb);