From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (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 0F9332BD030; Thu, 9 Apr 2026 03:11:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775704285; cv=none; b=WhJy81VsTZZD4D5PSz7GYJdTdW3dXomfAgtwUuv9dSyvFlZJXqVnSuQmMYz2vqL90nYWH/heSSujiTK3/KrbsYV7/XO1bnAOl4Eld1Q4QQHzdddKJYA23KSKWu7HP2tVUcvFVobFDMBsbTTeVHPhquxgqBTgWqjvrKA5aHUYIXA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775704285; c=relaxed/simple; bh=1GI+9d6w9kCMMnw522osxQF8zM+1ix2WSToIN+kEM8g=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=INRhH/O0yicHxKu3OwwVpYDWnjscfak6Eav0dEy468X86j7gCF4PRirLsKOq0AJicCUhHic0LKDw6fAy/Yr/saqOYKMkUNi0qtfv7F/Cat9TyYDuvwIPvbJcc8Vbg87wAzdsZIou5WhXKOzYTMVVLIGmciM6Gf9YSkuN257eZeQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=fp3ci9Ta; arc=none smtp.client-ip=91.218.175.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="fp3ci9Ta" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1775704278; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=Tv6vsULYE0pHAd8RGACfd9FryCGoTn/hw/neSKOVTiM=; b=fp3ci9TaSz7TnO4LHZpSluouaJgddH1w3KOW2ilM0GzrasFC/MRI1PZz5Y/bMs0S1FE3nP Ujn9SkGXtMuqSlVlvcWo/pg7IdrAl7e4rdKG4myBrkL+2PYlXRbvgznLWLQhe7bDqJYQ8e gADSv9nCl5RVzbd21NDAvPqSh8BH2sw= From: Qingfang Deng To: linux-ppp@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Qingfang Deng , Guillaume Nault , Wojciech Drewek , Tony Nguyen , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Cc: Paul Mackerras , Jaco Kroon , James Carlson , Marcin Szycik Subject: [PATCH net v3 1/2] flow_dissector: do not dissect PPPoE PFC frames Date: Thu, 9 Apr 2026 11:11:01 +0800 Message-ID: <20260409031107.616630-1-qingfang.deng@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT RFC 2516 Section 7 states that Protocol Field Compression (PFC) is NOT RECOMMENDED for PPPoE. In practice, pppd does not support negotiating PFC for PPPoE sessions, and the flow dissector driver has assumed an uncompressed frame until the blamed commit. During the review process of that commit [1], support for PFC is suggested. However, having a compressed (1-byte) protocol field means the subsequent PPP payload is shifted by one byte, causing 4-byte misalignment for the network header and an unaligned access exception on some architectures. The exception can be reproduced by sending a PPPoE PFC frame to an ethernet interface of a MIPS board, with RPS enabled, even if no PPPoE session is active on that interface: $ 0 : 00000000 80c40000 00000000 85144817 $ 4 : 00000008 00000100 80a75758 81dc9bb8 $ 8 : 00000010 8087ae2c 0000003d 00000000 $12 : 000000e0 00000039 00000000 00000000 $16 : 85043240 80a75758 81dc9bb8 00006488 $20 : 0000002f 00000007 85144810 80a70000 $24 : 81d1bda0 00000000 $28 : 81dc8000 81dc9aa8 00000000 805ead08 Hi : 00009d51 Lo : 2163358a epc : 805e91f0 __skb_flow_dissect+0x1b0/0x1b50 ra : 805ead08 __skb_get_hash_net+0x74/0x12c Status: 11000403 KERNEL EXL IE Cause : 40800010 (ExcCode 04) BadVA : 85144817 PrId : 0001992f (MIPS 1004Kc) Call Trace: [<805e91f0>] __skb_flow_dissect+0x1b0/0x1b50 [<805ead08>] __skb_get_hash_net+0x74/0x12c [<805ef330>] get_rps_cpu+0x1b8/0x3fc [<805fca70>] netif_receive_skb_list_internal+0x324/0x364 [<805fd120>] napi_complete_done+0x68/0x2a4 [<8058de5c>] mtk_napi_rx+0x228/0xfec [<805fd398>] __napi_poll+0x3c/0x1c4 [<805fd754>] napi_threaded_poll_loop+0x234/0x29c [<805fd848>] napi_threaded_poll+0x8c/0xb0 [<80053544>] kthread+0x104/0x12c [<80002bd8>] ret_from_kernel_thread+0x14/0x1c Code: 02d51821 1060045b 00000000 <8c640000> 3084000f 2c820005 144001a2 00042080 8e220000 To reduce the attack surface and maintain performance, do not process PPPoE PFC frames. While at it, avoid byte-swapping at runtime, restoring the original behavior. [1] https://patch.msgid.link/20220630231016.GA392@debian.home Fixes: 46126db9c861 ("flow_dissector: Add PPPoE dissectors") Signed-off-by: Qingfang Deng --- Changes in v3: Make ppp_proto_is_valid() private and fix kdoc warning, avoiding gotchas if some out-of-tree modules use this function. Link to v1: https://lore.kernel.org/netdev/20260407045743.174446-1-qingfang.deng@linux.dev/ include/linux/ppp_defs.h | 13 ------------- net/core/flow_dissector.c | 39 +++++++++++++++++++++++---------------- 2 files changed, 23 insertions(+), 29 deletions(-) diff --git a/include/linux/ppp_defs.h b/include/linux/ppp_defs.h index b7e57fdbd413..45c0947fa404 100644 --- a/include/linux/ppp_defs.h +++ b/include/linux/ppp_defs.h @@ -12,17 +12,4 @@ #define PPP_FCS(fcs, c) crc_ccitt_byte(fcs, c) -/** - * ppp_proto_is_valid - checks if PPP protocol is valid - * @proto: PPP protocol - * - * Assumes proto is not compressed. - * Protocol is valid if the value is odd and the least significant bit of the - * most significant octet is 0 (see RFC 1661, section 2). - */ -static inline bool ppp_proto_is_valid(u16 proto) -{ - return !!((proto & 0x0101) == 0x0001); -} - #endif /* _PPP_DEFS_H_ */ diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index 1b61bb25ba0e..64b843800370 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -1035,6 +1035,21 @@ static bool is_pppoe_ses_hdr_valid(const struct pppoe_hdr *hdr) return hdr->ver == 1 && hdr->type == 1 && hdr->code == 0; } +/** + * ppp_proto_is_valid - checks if PPP protocol is valid + * @proto: PPP protocol + * + * Assumes proto is not compressed. + * Protocol is valid if the value is odd and the least significant bit of the + * most significant octet is 0 (see RFC 1661, section 2). + * + * Return: Whether the PPP protocol is valid. + */ +static bool ppp_proto_is_valid(__be16 proto) +{ + return (proto & htons(0x0101)) == htons(0x0001); +} + /** * __skb_flow_dissect - extract the flow_keys struct and return it * @net: associated network namespace, derived from @skb if NULL @@ -1361,7 +1376,7 @@ bool __skb_flow_dissect(const struct net *net, struct pppoe_hdr hdr; __be16 proto; } *hdr, _hdr; - u16 ppp_proto; + __be16 ppp_proto; hdr = __skb_header_pointer(skb, nhoff, sizeof(_hdr), data, hlen, &_hdr); if (!hdr) { @@ -1374,27 +1389,19 @@ bool __skb_flow_dissect(const struct net *net, break; } - /* least significant bit of the most significant octet - * indicates if protocol field was compressed - */ - ppp_proto = ntohs(hdr->proto); - if (ppp_proto & 0x0100) { - ppp_proto = ppp_proto >> 8; - nhoff += PPPOE_SES_HLEN - 1; - } else { - nhoff += PPPOE_SES_HLEN; - } + ppp_proto = hdr->proto; + nhoff += PPPOE_SES_HLEN; - if (ppp_proto == PPP_IP) { + if (ppp_proto == htons(PPP_IP)) { proto = htons(ETH_P_IP); fdret = FLOW_DISSECT_RET_PROTO_AGAIN; - } else if (ppp_proto == PPP_IPV6) { + } else if (ppp_proto == htons(PPP_IPV6)) { proto = htons(ETH_P_IPV6); fdret = FLOW_DISSECT_RET_PROTO_AGAIN; - } else if (ppp_proto == PPP_MPLS_UC) { + } else if (ppp_proto == htons(PPP_MPLS_UC)) { proto = htons(ETH_P_MPLS_UC); fdret = FLOW_DISSECT_RET_PROTO_AGAIN; - } else if (ppp_proto == PPP_MPLS_MC) { + } else if (ppp_proto == htons(PPP_MPLS_MC)) { proto = htons(ETH_P_MPLS_MC); fdret = FLOW_DISSECT_RET_PROTO_AGAIN; } else if (ppp_proto_is_valid(ppp_proto)) { @@ -1412,7 +1419,7 @@ bool __skb_flow_dissect(const struct net *net, FLOW_DISSECTOR_KEY_PPPOE, target_container); key_pppoe->session_id = hdr->hdr.sid; - key_pppoe->ppp_proto = htons(ppp_proto); + key_pppoe->ppp_proto = ppp_proto; key_pppoe->type = htons(ETH_P_PPP_SES); } break; -- 2.43.0