From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 870504E4300; Tue, 13 Oct 2026 12:50:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791895810; cv=none; b=oP/znM0gx2O47NixtGTfh+MemtpEtGrGpSFma0sLtk/8ichlYOXqHnzMBy5R7kKRqJ55SN71nrLDRjuNIVLA0iCv9ueQLC1HFRlClwkq9flQ7cw4Z7gmGX5ixG5yRT8f9Uip+H1lCotONNdpacgJYgG56Y8PUrRcQ8XcCbenC08= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791895810; c=relaxed/simple; bh=6oUaZ5IoIJMJ1MzqenAIPSdYRlsvDs5ob1Gzu2KFmwg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=oeEelqgtD72PtQ/8rt4chR+zYjM9bSdEQ/wo3wVmhYL5S149vBX90EZP6ZcSoFQ0Vg7bbymSI8BJtq5nMYKm8+AMBtoSPKdIeA6QP+gxhB/0xf9fhZdKOHbplFUvM5MpHKcNlqwnQZoXCJ4YvSikmERlZzxsJ+2l1JFOvazQyQ4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=mgTsZ7RP; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="mgTsZ7RP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CB6131F0089D; Tue, 13 Oct 2026 12:50:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791895809; bh=Qiz6HvsiSYI69iYJztWNWn9e01rla6fVfNqUKGfiARM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=mgTsZ7RPpSKcqbmhWaFS+WuuBX9y6ASiotLshQoCsvG7LbVqUiR4Y2q8WEYPr5gDL Nz+Q8EpaoCitGMf7voalCf+GCcMlK8jbBPdusi8UFCR9qZ6eYSUNm4l3jQBqaexEid O4p3dHOnMxBZ/TBbOcyEkotp7ASYRTwmalkpiDB4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Quchaosheng , Willem de Bruijn , Jakub Kicinski Subject: [PATCH 6.12 399/497] net/packet: guard the ll header push in packet_rcv_spkt() Date: Tue, 13 Oct 2026 13:39:26 +0200 Message-ID: <20261013112917.362148376@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261013112907.864180619@linuxfoundation.org> References: <20261013112907.864180619@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Quchaosheng commit 28bc1ef699610ee09ce3d46a00552f5a0a0144bd upstream. packet_rcv_spkt() restores the link layer header with skb_push(skb, skb->data - skb_mac_header(skb)); That subtraction is only meaningful when the device actually has a link layer header. packet_rcv() and tpacket_rcv() both wrap it in dev_has_header(), which is also the predicate the block comment at the top of the file states the restore in terms of; packet_rcv_spkt() does not. commit d549699048b4 ("net/packet: fix packet receive on L3 devices without visible hard header") introduced the helper and changed the two call sites, and this one stayed behind. A device without a visible ll header can leave skb->mac_header at the 0xFFFF sentinel that __alloc_skb() initialises it to. A CAN skb does: init_can_skb() sets pkt_type and ip_summed but does not reset the headers, and commit 9f10374bb024 ("can: remove private CAN skb headroom infrastructure") dropped the skb_reset_*_header() calls that used to be there. skb_mac_header() is then 0xFFFF, the length becomes a large negative number and skb_push() reports it through skb_under_panic() -- from softirq context, so it is a full system panic even with panic_on_oops=0: skbuff: skb_under_panic: text:ffffffff8bd21bc1 len:-65455 put:-65471 head:... data:... tail:0x50 end:0x180 dev:can0 kernel BUG at net/core/skbuff.c:214! RIP: 0010:skb_panic+0x50/0x60 Call Trace: skb_push+0x38/0x40 packet_rcv_spkt+0xe1/0x170 __netif_receive_skb_core.constprop.0+0x7e8/0xd30 ... Kernel panic - not syncing: Fatal exception in interrupt The socket type is reachable: packet_create() accepts SOCK_PACKET alongside SOCK_RAW and SOCK_DGRAM behind the same CAP_NET_RAW check, and neither the socket length nor a capability check keeps it away from a CAN interface. The missing skb_reset_*_header() calls in init_can_skb() are a regression in their own right and are being fixed separately, but a packet socket should not turn a link layer that did not initialise its mac header into a kernel panic. Guard the push the way the other two receive paths do. Tested on v7.3-rc5 under QEMU with a slcan device on a pty, which is the driver RX path: vcan does not reproduce it, because can_send() resets the headers on the way out. One SOCK_PACKET socket bound to can0 and one frame written into the line discipline panics an unpatched kernel with the trace above; the same image with this patch prints no panic and powers off normally. Both kernels are this tree, defconfig plus CONFIG_CAN_SLCAN=y, differing only in this hunk. Fixes: d549699048b4 ("net/packet: fix packet receive on L3 devices without visible hard header") Cc: stable@vger.kernel.org Signed-off-by: Quchaosheng Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260928113108.2127215-1-quchaosheng000406@163.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/packet/af_packet.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1963,7 +1963,8 @@ static int packet_rcv_spkt(struct sk_buf spkt = &PACKET_SKB_CB(skb)->sa.pkt; - skb_push(skb, skb->data - skb_mac_header(skb)); + if (dev_has_header(dev)) + skb_push(skb, skb->data - skb_mac_header(skb)); /* * The SOCK_PACKET socket receives _all_ frames.