FAILED: patch "[PATCH] net: skbuff: propagate shared-frag marker in skb_zerocopy()" failed to apply to 5.10-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 79dc34beb1fdb3da79753e51e15c68591a2561fe
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026103057-payer-wobbly-83d2@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 79dc34beb1fdb3da79753e51e15c68591a2561fe Mon Sep 17 00:00:00 2001
From: Zizhen Liu <pointerliu@126.com>
Date: Thu, 22 Oct 2026 18:42:17 +0800
Subject: [PATCH] net: skbuff: propagate shared-frag marker in skb_zerocopy()

skb_zerocopy() moves frag descriptors from @from into @to and takes a
reference on each frag, but it does not copy skb_shinfo(from)->flags into
skb_shinfo(to)->flags.  A destination skb holding the same page-cache
backed frags as the source therefore reports skb_has_shared_frag() as
false.

That breaks the invariant relied on by later in-place writers.  ESP input
checks skb_has_shared_frag() before deciding whether an uncloned
nonlinear skb can skip skb_cow_data(); with the marker lost, an skb that
skb_zerocopy() built for nfnetlink_queue or for an openvswitch upcall is
decrypted in place, letting an unprivileged user write into the page
cache of a root-owned read-only file.

Propagate SKBFL_SHARED_FRAG when frag descriptors are copied, as done for
the other frag-transfer helpers.

Fixes: af2806f8f90a ("net: Export skb_zerocopy() to zerocopy from one skb to another")
Fixes: f4c50a4034e6 ("xfrm: esp: avoid in-place decrypt on shared skb frags")
Cc: stable@kernel.org
Signed-off-by: Zizhen Liu <pointerliu@126.com>
Reviewed-by: Eric Dumazet <edumazet@kernel.org>
Link: https://patch.msgid.link/20261022104217.1852191-1-pointerliu@126.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index eb9fcc4b1fd1..6a7c02b7653a 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3966,6 +3966,8 @@ skb_zerocopy(struct sk_buff *to, struct sk_buff *from, int len, int hlen)
 	}
 	skb_shinfo(to)->nr_frags = j;
 
+	skb_shinfo(to)->flags |= skb_shinfo(from)->flags & SKBFL_SHARED_FRAG;
+
 	if (i > 0 && from->unreadable)
 		to->unreadable = 1;