linux-kernel - [PATCH 5.10] gso: fix udp gso fraglist segmentation after pull from frag

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Message-ID: <20250328052315.1205798-1-sdl@nppct.ru>
Date: Fri, 28 Mar 2025 05:23:13 +0000
From: Alexey Nepomnyashih <sdl@...ct.ru>
To: "David S. Miller" <davem@...emloft.net>
Cc: Alexey Nepomnyashih <sdl@...ct.ru>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Jakub Kicinski <kuba@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <kafai@...com>,
	Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Willem de Bruijn <willemb@...gle.com>,
	Steffen Klassert <steffen.klassert@...unet.com>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org,
	bpf@...r.kernel.org,
	lvc-project@...uxtesting.org,
	stable@...r.kernel.org
Subject: [PATCH 5.10] gso: fix udp gso fraglist segmentation after pull from frag_list

From: Willem de Bruijn <willemb@...gle.com>

commit a1e40ac5b5e9077fe1f7ae0eb88034db0f9ae1ab upstream.

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: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
Signed-off-by: Willem de Bruijn <willemb@...gle.com>
Cc: stable@...r.kernel.org
Link: https://patch.msgid.link/20241001171752.107580-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Alexey Nepomnyashih <sdl@...ct.ru>
---
 net/ipv4/udp_offload.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index b6952b88b505..515d591d00b9 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -8,6 +8,7 @@
 
 #include <linux/skbuff.h>
 #include <net/udp.h>
+#include <net/ip6_checksum.h>
 #include <net/protocol.h>
 #include <net/inet_common.h>
 
@@ -269,8 +270,26 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 	__sum16 check;
 	__be16 newlen;
 
-	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 those 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;
+
+		uh = udp_hdr(gso_skb);
+		if (is_ipv6)
+			uh->check = ~udp_v6_check(gso_skb->len,
+						  &ipv6_hdr(gso_skb)->saddr,
+						  &ipv6_hdr(gso_skb)->daddr, 0);
+		else
+			uh->check = ~udp_v4_check(gso_skb->len,
+						  ip_hdr(gso_skb)->saddr,
+						  ip_hdr(gso_skb)->daddr, 0);
+	}
 
 	mss = skb_shinfo(gso_skb)->gso_size;
 	if (gso_skb->len <= sizeof(*uh) + mss)
-- 
2.43.0