From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Matt Fleming <mfleming@cloudflare.com>,
	=?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>,
	Lorenzo Bianconi <lorenzo@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.6 115/166] veth: convert frag_list skbs before running XDP
Date: Thu, 20 Aug 2026 16:56:14 +0200
Message-ID: <20260820145214.624047830@linuxfoundation.org>
In-Reply-To: <20260820145211.194104353@linuxfoundation.org>
References: <20260820145211.194104353@linuxfoundation.org>
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6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matt Fleming <mfleming@cloudflare.com>

[ Upstream commit d0d6415963040c401e7a7e4e482a698ba52448cb ]

A frag_list skb can reach veth with data_len set but nr_frags zero.
veth_convert_skb_to_xdp_buff() only converts skbs that are shared,
locked, have frags[], or do not have enough headroom. It later uses
skb_is_nonlinear() to decide whether to set XDP_FLAGS_HAS_FRAGS and
xdp_frags_size.

That exposes frag_list data to XDP as if it were stored in frags[], but
frags[] is empty. AF_XDP copy mode can then trust the bogus XDP fragment
metadata, walk an empty fragment entry, and crash in memcpy() from
__xsk_rcv().

Route non-linear skbs through skb_pp_cow_data() before exposing them to
XDP, and only advertise XDP frags when the resulting skb has frags[].
skb_copy_bits() already handles frag_list input, and skb_pp_cow_data()
builds frags[] output with skb_add_rx_frag(), which is the
representation XDP multi-buffer expects.

Fixes: 718a18a0c8a6 ("veth: Rework veth_xdp_rcv_skb in order to accept non-linear skb")
Cc: stable@vger.kernel.org
Signed-off-by: Matt Fleming <mfleming@cloudflare.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@toke.dk>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260722191925.2192070-1-matt@readmodwrite.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/veth.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -731,7 +731,7 @@ static int veth_convert_skb_to_xdp_buff(
 	u32 frame_sz;
 
 	if (skb_shared(skb) || skb_head_is_locked(skb) ||
-	    skb_shinfo(skb)->nr_frags ||
+	    skb_is_nonlinear(skb) ||
 	    skb_headroom(skb) < XDP_PACKET_HEADROOM) {
 		u32 size, len, max_head_size, off;
 		struct sk_buff *nskb;
@@ -808,7 +808,7 @@ static int veth_convert_skb_to_xdp_buff(
 	xdp_prepare_buff(xdp, skb->head, skb_headroom(skb),
 			 skb_headlen(skb), true);
 
-	if (skb_is_nonlinear(skb)) {
+	if (skb_shinfo(skb)->nr_frags) {
 		skb_shinfo(skb)->xdp_frags_size = skb->data_len;
 		xdp_buff_set_frags_flag(xdp);
 	} else {