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udp: fix potential use-after-free in tunnel segmentation

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__skb_udp_tunnel_segment() gets the UDP header before ensuring the
tunnel header is in the skb head. If the pull reallocates skb->head,
the saved UDP header pointer is no longer valid.

Get the UDP header after the pull to avoid a potential use-after-free.

Fixes: dbef491ebe ("udp: Use uh->len instead of skb->len to compute checksum in segmentation")
Signed-off-by: Xuanqiang Luo <luoxuanqiang@kylinos.cn>
Reviewed-by: Antoine Tenart <atenart@kernel.org>
Link: https://patch.msgid.link/20260730093554.68127-1-xuanqiang.luo@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Xuanqiang Luo
2026-07-30 17:35:54 +08:00
committed by Jakub Kicinski
parent d141f087b1
commit d0f86fb36e
1 changed files with 3 additions and 1 deletions
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4
net/ipv4/udp_offload.c
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@@ -178,17 +178,19 @@ static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
int tnl_hlen = skb_inner_mac_header(skb) - skb_transport_header(skb);
bool remcsum, need_csum, offload_csum, gso_partial;
struct sk_buff *segs = ERR_PTR(-EINVAL);
struct udphdr *uh = udp_hdr(skb);
u16 mac_offset = skb->mac_header;
__be16 protocol = skb->protocol;
u16 mac_len = skb->mac_len;
int udp_offset, outer_hlen;
struct udphdr *uh;
__wsum partial;
bool need_ipsec;
if (unlikely(!pskb_may_pull(skb, tnl_hlen)))
goto out;
uh = udp_hdr(skb);
/* Adjust partial header checksum to negate old length.
* We cannot rely on the value contained in uh->len as it is
* possible that the actual value exceeds the boundaries of the