From nobody Thu Oct 2 10:38:49 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E86FD2FFFB8; Thu, 18 Sep 2025 09:01:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758186115; cv=none; b=I6T0PHN4avfqjvqeLAx0+qpKfSolLThJCrzk705timqAQ5N4ebeUA2EwQNYPH2X65sQYQVMICHnkJKo9q9lGOtP2bS9UC8cQwRJOo9WcS2SkHicAxWXZ+hdF76qCv9uYhB53pIHriEsXor9TxROyUQBapAcgOTdeti2Z9GaTyL4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758186115; c=relaxed/simple; bh=mGSWa58npvsbMCZz/6vmp8p/XePk3TJBfYof7NGs8oU=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=uJYvb5huZkMXsN5QLA/tEdVR2dc52L6wIXxfvMOeFwoLco5q7PqNTwa3dXMV+LYZ/3a+xVURwOajMU34tIFHl72z+0h85SVA4fWaUa+Qvc4n07dUf/cUL1K6pSQrYMUCxu2hLei2CvexMZUcKq+o6eeCnPo3ih99HeJutpI3oNE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LykDXyf9; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LykDXyf9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 48F37C4CEE7; Thu, 18 Sep 2025 09:01:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758186114; bh=mGSWa58npvsbMCZz/6vmp8p/XePk3TJBfYof7NGs8oU=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=LykDXyf9viuasSfBsno2kiu+GBRZ9k02IgoUx32ATpI36+DMYYge8IsVktJ9Y0hCh itVkhBj/FxyvYIGA/ZC66LiXHhEY+BCGEcLOG6DriQ7pntaLTQzj4mT9MFxuXrdZWR WTlQZ+3uh7vQZJciFKtbeaQAWg2Fj5Z3CKaHH9DV5J7ZDeO0BOJgzGqIQYA6AZVHbu KWkWpLNsRJtCOKlUzhICLsYmMJPHWa2AvjT1JqQAK0x8A3ZI5V0GAdmzBzy5aAuZnR Ms3juopOsxXJRCs9uV5hU1+6dquREhGtGXFRjkpIAe/5CmUGaA6xiBdTsK6cje+hEh 6JCP5JTck0aAw== From: Vincent Mailhol Date: Thu, 18 Sep 2025 18:00:26 +0900 Subject: [PATCH 3/4] can: sun4i_can: populate ndo_change_mtu() to prevent buffer overflow Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250918-can-fix-mtu-v1-3-0d1cada9393b@kernel.org> References: <20250918-can-fix-mtu-v1-0-0d1cada9393b@kernel.org> In-Reply-To: <20250918-can-fix-mtu-v1-0-0d1cada9393b@kernel.org> To: Marc Kleine-Budde , Oliver Hartkopp Cc: Arunachalam Santhanam , Akshay Bhat , Wolfgang Grandegger , Chen-Yu Tsai , Jernej Skrabec , Samuel Holland , Maxime Ripard , Gerhard Bertelsmann , Yasushi SHOJI , =?utf-8?q?Remigiusz_Ko=C5=82=C5=82=C4=85taj?= , linux-can@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev, Vincent Mailhol X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=2683; i=mailhol@kernel.org; h=from:subject:message-id; bh=mGSWa58npvsbMCZz/6vmp8p/XePk3TJBfYof7NGs8oU=; b=owGbwMvMwCV2McXO4Xp97WbG02pJDBmnTxWZTgw4VM999eMKhiW/mgPzTVdd92X5/OeGtJvF4 gvHcjqud5SyMIhxMciKKbIsK+fkVugo9A479NcSZg4rE8gQBi5OAZjIfQZGhv9126JX8G42aY3J mbiI+0nZJbvFB699Tqvivdr3J7Ca8z8jwwTdeWUXmvIuqQQHsiS6Km2sXf3IRa/fUMf80IctX55 PZwEA X-Developer-Key: i=mailhol@kernel.org; a=openpgp; fpr=ED8F700574E67F20E574E8E2AB5FEB886DBB99C2 Sending an PF_PACKET allows to bypass the CAN framework logic and to directly reach the xmit() function of a CAN driver. The only check which is performed by the PF_PACKET framework is to make sure that skb->len fits the interface's MTU. Unfortunately, because the sun4i_can driver does not populate its net_device_ops->ndo_change_mtu(), it is possible for an attacker to configure an invalid MTU by doing, for example: $ ip link set can0 mtu 9999 After doing so, the attacker could open a PF_PACKET socket using the ETH_P_CANXL protocol: socket(PF_PACKET, SOCK_RAW, htons(ETH_P_CANXL)) to inject a malicious CAN XL frames. For example: struct canxl_frame frame =3D { .flags =3D 0xff, .len =3D 2048, }; The CAN drivers' xmit() function are calling can_dev_dropped_skb() to check that the skb is valid, unfortunately under above conditions, the malicious packet is able to go through can_dev_dropped_skb() checks: 1. the skb->protocol is set to ETH_P_CANXL which is valid (the function does not check the actual device capabilities). 2. the length is a valid CAN XL length. And so, sun4ican_start_xmit() receives a CAN XL frame which it is not able to correctly handle and will thus misinterpret it as a CAN frame. This can result in a buffer overflow. The driver will consume cf->len as-is with no further checks on this line: dlc =3D cf->len; Here, cf->len corresponds to the flags field of the CAN XL frame. In our previous example, we set canxl_frame->flags to 0xff. Because the maximum expected length is 8, a buffer overflow of 247 bytes occurs a couple line below when doing: for (i =3D 0; i < dlc; i++) writel(cf->data[i], priv->base + (dreg + i * 4)); Populate net_device_ops->ndo_change_mtu() to ensure that the interface's MTU can not be set to anything bigger than CAN_MTU. By fixing the root cause, this prevents the buffer overflow. Fixes: 0738eff14d81 ("can: Allwinner A10/A20 CAN Controller support - Kerne= l module") Signed-off-by: Vincent Mailhol --- drivers/net/can/sun4i_can.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/net/can/sun4i_can.c b/drivers/net/can/sun4i_can.c index 6fcb301ef611d0c8bdb8720aaa77dc78950123d6..53bfd873de9bdecaf6923049007= f9efd71289dd3 100644 --- a/drivers/net/can/sun4i_can.c +++ b/drivers/net/can/sun4i_can.c @@ -768,6 +768,7 @@ static const struct net_device_ops sun4ican_netdev_ops = =3D { .ndo_open =3D sun4ican_open, .ndo_stop =3D sun4ican_close, .ndo_start_xmit =3D sun4ican_start_xmit, + .ndo_change_mtu =3D can_change_mtu, }; =20 static const struct ethtool_ops sun4ican_ethtool_ops =3D { --=20 2.49.1