Please apply commit 4db79a322db8 ("net: gro: don't merge zcopy skbs") to 6.1.y

[Salvatore Bonaccorso <carnil@debian.org>]

Hi

4db79a322db8 ("net: gro: don't merge zcopy skbs") was backported to
various stable series (6.6, 6.12, 6.18 and 7.0) but not to 6.1.y as it
does not apply cleanly. With adjusting context the change applies,
proposed change below.

Does that looks good, and can you pick up the change as well for the
6.1.y series?

Regards,
Salvatore

From d6ad94fa8c6ff9c191e5545bc6277d2e3c75b811 Mon Sep 17 00:00:00 2001
From: Sabrina Dubroca <sd@queasysnail.net>
Date: Wed, 20 May 2026 22:44:42 +0200
Subject: [PATCH] net: gro: don't merge zcopy skbs

[ Upstream commit 4db79a322db8c97f7b73b8a347395ef4d685eb40 ]

skb_gro_receive() can currently copy frags between the source and GRO
skb, without checking the zerocopy status, and in particular the
SKBFL_MANAGED_FRAG_REFS flag.

When SKBFL_MANAGED_FRAG_REFS is set, the skb doesn't hold a reference
on the pages in shinfo->frags. Appending those frags to another skb's
frags without fixing up the page refcount can lead to UAF.

When either the last skb in the GRO chain (the one we would append
frags to) or the source skb is zerocopy, don't merge the skbs.

Fixes: 753f1ca4e1e5 ("net: introduce managed frags infrastructure")
Reported-by: Huzaifa Sidhpurwala <huzaifas@redhat.com>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/c3b7f906bbfcbdfd7b4fa9d6c18a438870df85be.1779307748.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[Salvatore Bonaccorso: Adjust for context in 6.1.y series without
e8d4d34df715 ("net: Add netif_get_gro_max_size helper for GRO")]
Signed-off-by: Salvatore Bonaccorso <carnil@debian.org>
---
 net/core/gro.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/gro.c b/net/core/gro.c
index ea6571c01faa..c5a9733d929a 100644
--- a/net/core/gro.c
+++ b/net/core/gro.c
@@ -171,6 +171,9 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
 	if (p->pp_recycle != skb->pp_recycle)
 		return -ETOOMANYREFS;
 
+	if (skb_zcopy(p) || skb_zcopy(skb))
+		return -ETOOMANYREFS;
+
 	/* pairs with WRITE_ONCE() in netif_set_gro_max_size() */
 	gro_max_size = READ_ONCE(p->dev->gro_max_size);
 
-- 
2.53.0