bottlerocket-kernel-kit/packages/kernel-6.1/1008-ipv4-account-for-fraggap-on-the-paged-allocation-pat.patch at 74a0962f1704be3f6ca7a64f03110021e3d216e4 · bottlerocket-os/bottlerocket-kernel-kit · GitHub

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From 40d30498c8ea3e3495642f8cc5c263cb13d55b76 Mon Sep 17 00:00:00 2001
From: Wongi Lee <qw3rtyp0@gmail.com>
Date: Tue, 16 Jun 2026 22:38:29 +0900
Subject: [PATCH] ipv4: account for fraggap on the paged allocation path

In __ip_append_data(), when the paged-allocation branch is taken,
alloclen and pagedlen are computed as

	alloclen = fragheaderlen + transhdrlen;
	pagedlen = datalen - transhdrlen;

datalen already includes fraggap, but the fraggap bytes carried over
from the previous skb are copied into the new skb's linear area at
offset transhdrlen by the subsequent skb_copy_and_csum_bits(). The
linear area is therefore undersized by fraggap bytes while pagedlen is
overstated by the same amount.

The non-paged branch sets alloclen to fraglen, which already accounts
for fraggap because datalen does. Bring the paged branch in line by
adding fraggap to alloclen and subtracting it from pagedlen.

After this adjustment, copy no longer collapses to -fraggap on the
paged path, so remove the stale comment describing that old arithmetic.

Fixes: 8eb77cc73977 ("ipv4: avoid partial copy for zc")
Signed-off-by: Jungwoo Lee <jwlee2217@gmail.com>
Signed-off-by: Wongi Lee <qw3rtyp0@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/ajFR1eLAIs42TN3g@DESKTOP-19IMU7U.localdomain
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

[Resolve merge conflict caused by missing 5204ccbfa223 which wraps
INDIRECT_CALL_1. Resolve the merge conflict by keeping current logic.]

Signed-off-by: Stanislav Uschakow <suschako@amazon.de>
(cherry picked from commit d11d68214a0afab174ab8f712890452adcf7c196)
---
 net/ipv4/ip_output.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index f5a2ad2b2dbdf..778214137e4a2 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1117,8 +1117,8 @@ static int __ip_append_data(struct sock *sk,
 				  !(rt->dst.dev->features & NETIF_F_SG)))
 				alloclen = fraglen;
 			else {
-				alloclen = fragheaderlen + transhdrlen;
-				pagedlen = datalen - transhdrlen;
+				alloclen = fragheaderlen + transhdrlen + fraggap;
+				pagedlen = datalen - transhdrlen - fraggap;
 			}

 			alloclen += alloc_extra;
--
2.52.0