[PATCH net v5] xfrm: iptfs: preserve shared-frag marker in iptfs_consume_frags()

[PATCH net v5] 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 # 6.14+
Signed-off-by: Takao Sato <takaosato1997@gmail.com>
---
Changes since v4:
- Rebased onto the ipsec tree, as requested by Steffen Klassert. No
  functional changes; only the diff context was regenerated.

Changes since v3:
- Corrected Cc: stable tag from "# 6.8+" to "# 6.14+". IPTFS was
  introduced in v6.14, so earlier stable branches do not need this
  fix. Pointed out by Pedro Falcato.

Changes since v2:
- Removed security impact paragraph from commit message as requested
  by Steffen Klassert.

 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

Re: [PATCH net v5] xfrm: iptfs: preserve shared-frag marker in iptfs_consume_frags()

[Steffen Klassert]

On Tue, May 26, 2026 at 01:09:57PM -0300, Takao Sato wrote:
> 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>
> ---
> Changes since v4:
> - Rebased onto the ipsec tree, as requested by Steffen Klassert. No
>   functional changes; only the diff context was regenerated.
> 
> Changes since v3:
> - Corrected Cc: stable tag from "# 6.8+" to "# 6.14+". IPTFS was
>   introduced in v6.14, so earlier stable branches do not need this
>   fix. Pointed out by Pedro Falcato.
> 
> Changes since v2:
> - Removed security impact paragraph from commit message as requested
>   by Steffen Klassert.
> 
>  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;

Sashiko found some issues in iptfs. It is not directly related to this
patch but looks valid:

https://sashiko.dev/#/patchset/20260526160957.1497109-1-takaosato1997%40gmail.com

Chris can you have a look at it?