[PATCH net v3] xfrm: iptfs: preserve shared-frag marker in iptfs_consume_frags()

[PATCH net v3] xfrm: iptfs: preserve shared-frag marker in iptfs_consume_frags()

[Takao Sato]

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 # 6.8+
Signed-off-by: Takao Sato <takaosato1997@gmail.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 97bc979e5..4db85e158 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

Re: [PATCH net v3] xfrm: iptfs: preserve shared-frag marker in iptfs_consume_frags()

[Christian Hopps]

Takao Sato <takaosato1997@gmail.com> writes:

> 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 # 6.8+
> Signed-off-by: Takao Sato <takaosato1997@gmail.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 97bc979e5..4db85e158 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;

LGTM, Thanks!

Reviewed-by: Christian Hopps <chopps@labn.net>