From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Maoyi Xie <maoyixie.tju@gmail.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 112/272] net: thunderbolt: Fix frags[] overflow by bounding frame_count
Date: Thu, 20 Aug 2026 16:54:56 +0200
Message-ID: <20260820145234.629966157@linuxfoundation.org>
In-Reply-To: <20260820145231.229664293@linuxfoundation.org>
References: <20260820145231.229664293@linuxfoundation.org>
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5.15-stable review patch.  If anyone has any objections, please let me know.

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

From: Maoyi Xie <maoyixie.tju@gmail.com>

[ Upstream commit 55d9895f89970501fe126d1026b586b04a224c27 ]

tbnet_poll() assembles a multi-frame ThunderboltIP packet into one skb. The
first frame goes into the skb linear area and every further frame is added as
a page fragment.

	skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
			page, hdr_size, frame_size,
			TBNET_RX_PAGE_SIZE - hdr_size);

A packet of frame_count frames therefore ends up with frame_count - 1
fragments. tbnet_check_frame() only bounds the peer supplied frame_count to
TBNET_RING_SIZE / 4 (64), which is far above MAX_SKB_FRAGS (17 by default). A
peer that sends a packet of 19 or more small frames pushes nr_frags past
MAX_SKB_FRAGS, so skb_add_rx_frag() writes past skb_shinfo()->frags[] and
corrupts memory after the shared info.

Tighten the start of packet bound to MAX_SKB_FRAGS + 1 so a packet can never
produce more fragments than frags[] can hold. This matches the recent skb
frags overflow fixes in other receive paths, for example f0813bcd2d9d ("net:
wwan: t7xx: fix potential skb->frags overflow in RX path") and 600dc40554dc
("net: usb: cdc-phonet: fix skb frags[] overflow in rx_complete()").

Fixes: e69b6c02b4c3 ("net: Add support for networking over Thunderbolt cable")
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Link: https://patch.msgid.link/178163152194.2486768.14724194232649760778@maoyixie.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/thunderbolt.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/net/thunderbolt.c
+++ b/drivers/net/thunderbolt.c
@@ -756,8 +756,12 @@ static bool tbnet_check_frame(struct tbn
 		return true;
 	}
 
-	/* Start of packet, validate the frame header */
-	if (frame_count == 0 || frame_count > TBNET_RING_SIZE / 4) {
+	/* Start of packet, validate the frame header. tbnet_poll() puts the
+	 * first frame in the skb linear area and every further frame in a page
+	 * fragment, so a packet may not span more than MAX_SKB_FRAGS + 1 frames
+	 * without overflowing skb_shinfo()->frags[].
+	 */
+	if (frame_count == 0 || frame_count > MAX_SKB_FRAGS + 1) {
 		net->stats.rx_length_errors++;
 		return false;
 	}