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udp: gso: Fix handling checksum in __udp_gso_segment

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The cited commit started using msslen for uh->len, but still uses newlen
to adjust uh->check. Although the checksum is ignored in most cases due
to the hardware offload, __udp_gso_segment attempts to maintain the
correct one. Fix uh->check and adjust it by the right value.

Additionally, after the fix, newlen becomes assigned and unused before
the loop. The code can be simplified a bit if mss adjustment is dropped,
so that newlen becomes equal to msslen before the loop, and msslen can
be also dropped, saving a few lines of code.

This brings us back to one variable, drops an unneeded arithmetic for
mss, and fixes the UDP checksum.

Fixes: b10b446ce7 ("udp: gso: Use single MSS length in UDP header for GSO_PARTIAL")
Signed-off-by: Alice Mikityanska <alice@isovalent.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Link: https://patch.msgid.link/20260518062250.3019914-2-gal@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Alice Mikityanska 2026-05-18 09:22:49 +03:00 committed by Jakub Kicinski
parent dc416e32ba
commit 5f17ae0f59
1 changed files with 2 additions and 11 deletions
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13
net/ipv4/udp_offload.c
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@ -482,11 +482,11 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
struct sock *sk = gso_skb->sk;
unsigned int sum_truesize = 0;
struct sk_buff *segs, *seg;
__be16 newlen, msslen;
struct udphdr *uh;
unsigned int mss;
bool copy_dtor;
__sum16 check;
__be16 newlen;
int ret = 0;
mss = skb_shinfo(gso_skb)->gso_size;
@ -555,15 +555,6 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
return segs;
}
msslen = htons(sizeof(*uh) + mss);
/* GSO partial and frag_list segmentation only requires splitting
* the frame into an MSS multiple and possibly a remainder, both
* cases return a GSO skb. So update the mss now.
*/
if (skb_is_gso(segs))
mss *= skb_shinfo(segs)->gso_segs;
seg = segs;
uh = udp_hdr(seg);
@ -586,7 +577,7 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
if (!seg->next)
break;
uh->len = msslen;
uh->len = newlen;
uh->check = check;
if (seg->ip_summed == CHECKSUM_PARTIAL)