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 3E7AB3FC5D1; Wed, 20 May 2026 18:43:16 +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=1779302597; cv=none; b=m9zMz+2RRjp8elpejgYMyubtfl0lliWGVGDI5IDbpeODYhbSk6kICiKHwW8sOUi2TK/tQlJ8rS1R/frbKmGeZwfSMX2aTH5H2hFICpXYW4pjVuwt3MMiYFJzEAfa1SnG/yudDHF/BxxUQsEui2fPgOnULYdX86DE22Rz6Po57Rw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779302597; c=relaxed/simple; bh=p4hUuUenbcVMI3BTj7tPmS1CwHjcTGvIHEGXmoY+hM0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=DCTst2uYDdNlydYttBG6XjmnYSHsIn4dEGzWJBFDREZhFdBuLeqwfgILqcHXYp4wgm53zC30r+Bsyg2lpuDBukmKv7uCJVOVACqvHgiAznQtO80mmvLe1BhBsC6i0fYPyiWNXOSKtdDHmdK0GEeEJRrEjnRMZNsQTXmc7JUWzqQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=r6McLOhc; 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="r6McLOhc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CD1F81F00893; Wed, 20 May 2026 18:43:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1779302596; bh=oXErK6f5EBInueMOB9dccw1hfUvKyYkx9buqhuDP3YE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=r6McLOhcaGdjzeZG4vjirXeelfBrfy99pTFGiMEnRix79xPTycxVE4YJ3W2sRtMyd sou+j2mKuFBs0uhhgiWhC1f2u2dLlmSoNHqxnzOA66hnsIDcY+Njkd9Jq9rLdzSqCk kVl4D1BV7akfLHwiX+8KWjPUZA7jzXvGGbw+tTzg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Qingfang Deng , Simon Horman , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.6 327/508] pppoe: drop PFC frames Date: Wed, 20 May 2026 18:22:30 +0200 Message-ID: <20260520162105.719838642@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520162058.573354582@linuxfoundation.org> References: <20260520162058.573354582@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Qingfang Deng [ Upstream commit cc1ff87bce1ccd38410ab10960f576dcd17db679 ] 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 current PPPoE driver assumes an uncompressed (2-byte) protocol field. However, the generic PPP layer function ppp_input() is not aware of the negotiation result, and still accepts PFC frames. If a peer with a broken implementation or an attacker sends a frame with a compressed (1-byte) protocol field, the subsequent PPP payload is shifted by one byte. This causes the network header to be 4-byte misaligned, which may trigger unaligned access exceptions on some architectures. To reduce the attack surface, drop PPPoE PFC frames. Introduce ppp_skb_is_compressed_proto() helper function to be used in both ppp_generic.c and pppoe.c to avoid open-coding. Fixes: 7fb1b8ca8fa1 ("ppp: Move PFC decompression to PPP generic layer") Signed-off-by: Qingfang Deng Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260415022456.141758-2-qingfang.deng@linux.dev Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- drivers/net/ppp/ppp_generic.c | 2 +- drivers/net/ppp/pppoe.c | 8 +++++++- include/linux/ppp_defs.h | 16 ++++++++++++++++ 3 files changed, 24 insertions(+), 2 deletions(-) diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index 7c863cb99383b..2b5843d14cbb8 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -2245,7 +2245,7 @@ ppp_do_recv(struct ppp *ppp, struct sk_buff *skb, struct channel *pch) */ static void __ppp_decompress_proto(struct sk_buff *skb) { - if (skb->data[0] & 0x01) + if (ppp_skb_is_compressed_proto(skb)) *(u8 *)skb_push(skb, 1) = 0x00; } diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c index 96cca4ee470a4..bc726b54ca745 100644 --- a/drivers/net/ppp/pppoe.c +++ b/drivers/net/ppp/pppoe.c @@ -425,7 +425,7 @@ static int pppoe_rcv(struct sk_buff *skb, struct net_device *dev, if (skb_mac_header_len(skb) < ETH_HLEN) goto drop; - if (!pskb_may_pull(skb, sizeof(struct pppoe_hdr))) + if (!pskb_may_pull(skb, PPPOE_SES_HLEN)) goto drop; ph = pppoe_hdr(skb); @@ -435,6 +435,12 @@ static int pppoe_rcv(struct sk_buff *skb, struct net_device *dev, if (skb->len < len) goto drop; + /* skb->data points to the PPP protocol header after skb_pull_rcsum. + * Drop PFC frames. + */ + if (ppp_skb_is_compressed_proto(skb)) + goto drop; + if (pskb_trim_rcsum(skb, len)) goto drop; diff --git a/include/linux/ppp_defs.h b/include/linux/ppp_defs.h index b7e57fdbd4139..b1d1f46d7d3be 100644 --- a/include/linux/ppp_defs.h +++ b/include/linux/ppp_defs.h @@ -8,6 +8,7 @@ #define _PPP_DEFS_H_ #include +#include #include #define PPP_FCS(fcs, c) crc_ccitt_byte(fcs, c) @@ -25,4 +26,19 @@ static inline bool ppp_proto_is_valid(u16 proto) return !!((proto & 0x0101) == 0x0001); } +/** + * ppp_skb_is_compressed_proto - checks if PPP protocol in a skb is compressed + * @skb: skb to check + * + * Check if the PPP protocol field is compressed (the least significant + * bit of the most significant octet is 1). skb->data must point to the PPP + * protocol header. + * + * Return: Whether the PPP protocol field is compressed. + */ +static inline bool ppp_skb_is_compressed_proto(const struct sk_buff *skb) +{ + return unlikely(skb->data[0] & 0x01); +} + #endif /* _PPP_DEFS_H_ */ -- 2.53.0