[PATCH 1/6] xfrm: iptfs: preserve shared-frag marker in iptfs_consume_frags()

[Steffen Klassert <steffen.klassert@secunet.com>]

From: Takao Sato <takaosato1997@gmail.com>

iptfs_consume_frags() transfers paged fragments from one socket buffer
to another but fails to propagate the SKBFL_SHARED_FRAG flag. This is
the same class of bug that was fixed in skb_try_coalesce() for
CVE-2026-46300: when fragments backed by read-only page-cache pages are
merged, the marker indicating their shared nature must be preserved so
that ESP can decide correctly whether in-place encryption is safe.

Apply the same two-line fix used in skb_try_coalesce() to
iptfs_consume_frags().

Fixes: b96ba312e21c ("xfrm: iptfs: share page fragments of inner packets")
Cc: stable@vger.kernel.org # 6.14+
Signed-off-by: Takao Sato <takaosato1997@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
 net/xfrm/xfrm_iptfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/xfrm/xfrm_iptfs.c b/net/xfrm/xfrm_iptfs.c
index 6c6bbc040517..62ba828632f1 100644
--- a/net/xfrm/xfrm_iptfs.c
+++ b/net/xfrm/xfrm_iptfs.c
@@ -2168,6 +2168,8 @@ static void iptfs_consume_frags(struct sk_buff *to, struct sk_buff *from)
 	memcpy(&toi->frags[toi->nr_frags], fromi->frags,
 	       sizeof(fromi->frags[0]) * fromi->nr_frags);
 	toi->nr_frags += fromi->nr_frags;
+	if (fromi->nr_frags)
+		toi->flags |= fromi->flags & SKBFL_SHARED_FRAG;
 	fromi->nr_frags = 0;
 	from->data_len = 0;
 	from->len = 0;
-- 
2.43.0