From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yx1-f45.google.com (mail-yx1-f45.google.com [74.125.224.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0F9F63F482F for ; Thu, 23 Jul 2026 21:23:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.224.45 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784841784; cv=none; b=EQ8h5s3kRl/i7q3+4JmfOu3WPQ3dsogfw8mKln2nLgl29VYebhurrcM/Vm3VMmV+QCKZYW6JHgcWrGf3G9o0Xcwl5KYYg9e0qoPeNhfNUZ2wFv085Q9lbuQdWzea3fuQlVjVHG/NZjHA5AHQzfK+kWjipnqm4ejp2ILKSq5ke/A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784841784; c=relaxed/simple; bh=haxoTexRbNT3Ih6fcspZyW2FGvcgo6DcA9WcvwhndhE=; h=Date:From:To:Cc:Message-ID:In-Reply-To:References:Subject: Mime-Version:Content-Type; b=Zgxygc1vBIfPyS9paKyebtoTuiZHK1MEewS8H0ckDKaqvnAoq3+H1SmNiua7o9ih8Ez3i9RIAcCIlO9aH+uIdesZmWEi9H2dHdRBCn2J8qL07ZBigOU/4KDvnNjW11am6K4pLabEepedOKkxJ0Rjpv2yr3HXh6ettFM1Kujox6s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=P2pzC/YL; arc=none smtp.client-ip=74.125.224.45 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="P2pzC/YL" Received: by mail-yx1-f45.google.com with SMTP id 956f58d0204a3-6689402c7bfso877125d50.1 for ; Thu, 23 Jul 2026 14:23:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1784841781; x=1785446581; darn=vger.kernel.org; h=content-transfer-encoding:content-type:mime-version:subject :references:in-reply-to:message-id:cc:to:from:date:from:to:cc :subject:date:message-id:reply-to:content-type; bh=xGlxBC5SjfZiRwDCCi1VHk7rw5dfR+3uY48owyOZVBg=; b=P2pzC/YL6ykygsCnfBbL7la9UEVPq4fO10utvJE8kQFz3TPIlQj5VcA1ZH9wxO64TB AeC3czdDjOBIFXiKSxyfYD+LEzG9s4gKOWyrLk62e1DwGGazyLy0ZDA8CfSRVn/yRgi6 yWsroDvlJedAJRecceOOfMczVTWucqEHnyfmMkRrsSX83B4Z4/6L8VvO575up4Mb7xIh SPZsAVozjcv7ibAY381drmFpXTfp4EOwS0t4wH1Vlvt/qhjt9VOlk2X9nSVnoUolIVD4 ti7AaUXvKfauCrjmvywXL8lRFBvG1V5Rxzm1lT8sdN7Ic3QBEs7u1vrwNR+zjK+Xe0Dm H0yQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1784841781; x=1785446581; h=content-transfer-encoding:content-type:mime-version:subject :references:in-reply-to:message-id:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=xGlxBC5SjfZiRwDCCi1VHk7rw5dfR+3uY48owyOZVBg=; b=U6E0a+KENJw3kmQXptoinbJghO0zbKlJSjXLGt0rH9PxFtrHwM9GDyT+liq6FSHOVY +HHEZ6rPko1CLRxZpch/B1+XO8UT7GxhOVa7Kf8cAK+AoJOIA3CxazgEZQLBSJStekUo gQ/5RDPDdIXn/gdnQLtH3FhhK+F/brv0jOLnmti7l4FrODG0pBNW4NajXbu3uErFgLO8 2MqL9/yvO9l3R7h3WKAlR4nJbLfdfu0umyJjoGnTOiDoStKTUGcvI6S6R8V/ly0AUPSx m8u0+mBmNXwVghTTFG+zaI2JQOvUgOb25n8PQur/VaksSczXPcW4fgt5UbKe3NXbK/8d BasQ== X-Forwarded-Encrypted: i=1; AHgh+Rp3eL+6LATeG50wX41HkkcxIf9Ynbul51U9fnZFbmGEsFxxe+5p5UUz0MPfPv2ThbFFcDEIgbjrdQ/isGA=@vger.kernel.org X-Gm-Message-State: AOJu0YyrDyz7ZpRQYY6AxqGSS6bqRQ9kljTJE/EfugEtX5mu7Wd5QYyf rjDUmsGu0jZnuWWddTbzurhByBEPeGXZOeFP1RnJqs1uMEvQeAH1pnHd X-Gm-Gg: AR+sD12dksOyoLFbZ43vOnGM+eza2GO4aTFMexxNziWxDfJiowzF1lcRxO30PC581vS 7fk5ZB4Te3KCrmm0/8RmLRhd3fPAJmobcEE5EU4qcC/3x0u8w7Ev/lHfddbcs3Pecp7SHiH3AI6 nP8InZNNyExK49KrC0JzvKHpHe02VYR0pFQ1XZiFN1y7DKlE8buFJTW+SjImgEMeMzBbT4h4NlX GdVyPMxIMw/rfvImndz1GkH/SrybJ7q8Qr/z/PyZaTMYuxnoDNYtUscZmPSdMC7DgS3LhcRaeW9 4iboUWRRgrFZpmdWpoNQDeK9z8zZ1TgXL3yilRdC/5pcNkr9PPLf7RRPtQIyoNVkaWkcfygjj6s 8WJ6Zb8ZhRomA9ACZ7T34N3VsqnAGqdkPVSrKm/JZKLyJNhSy6IYvis7kwK3qCiv9dfrKzmneZj sxYw9nuY/siFRFbBULapeZqf67+KkKDtJlW2/aPakairuysCYQxMLhfng= X-Received: by 2002:a05:690e:4384:b0:667:bf78:e8b1 with SMTP id 956f58d0204a3-668a4ba75c9mr919504d50.10.1784841780919; Thu, 23 Jul 2026 14:23:00 -0700 (PDT) Received: from gmail.com (172.235.85.34.bc.googleusercontent.com. [34.85.235.172]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-6689766347csm3215255d50.10.2026.07.23.14.23.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jul 2026 14:23:00 -0700 (PDT) Date: Thu, 23 Jul 2026 17:22:59 -0400 From: Willem de Bruijn To: Willem de Bruijn , Doruk Tan Ozturk , Willem de Bruijn , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , Sabrina Dubroca , Vladimir Oltean , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Doruk Tan Ozturk Message-ID: In-Reply-To: References: <20260723020337.19040-1-doruk@0sec.ai> Subject: Re: [PATCH net] net/packet: reset the MAC header on the packet-socket transmit path 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: 7bit Willem de Bruijn wrote: > Doruk Tan Ozturk wrote: > > packet_parse_headers() resets the MAC header only for a SOCK_RAW frame > > whose socket did not bind a protocol: > > > > if ((!skb->protocol || skb->protocol == htons(ETH_P_ALL)) && > > sock->type == SOCK_RAW) { > > skb_reset_mac_header(skb); > > skb->protocol = dev_parse_header_protocol(skb); > > } > > > > Every other outgoing packet-socket frame therefore reaches > > ndo_start_xmit() with the MAC header unset: a SOCK_RAW socket bound to a > > The normal __dev_queue_xmit calls skb_reset_mac_header. > > This therefore only applies to the dev_direct_xmit path. > > > specific protocol (for example socket(AF_PACKET, SOCK_RAW, > > htons(ETH_P_IP))), any SOCK_DGRAM frame (its header is built by > > dev_hard_header(), which does not set mac_header), and the legacy > > SOCK_PACKET path. A driver that reads eth_hdr(skb) on transmit then > > dereferences skb->head + (u16)~0, an out-of-bounds access about 64 KiB > > past the head. > > This is not currently an expected invariant, but I see from a comment > below the --- that this approach is proposed instead of fixing up the > buggy drivers. > > > > > This is the same class fixed for one consumer in commit f5089008f90c > > ("macsec: do not read an unset MAC header in macsec_encrypt()"); other > > TX .xmit paths that read eth_hdr(skb)->h_dest (several DSA taggers, > > ibmveth, sja1105, the atlantic PTP path) have the same problem. > > > > packet_parse_headers() runs only on the transmit path > > (packet_sendmsg_spkt(), tpacket_fill_skb(), packet_snd()), and there > > skb->data is the start of the L2 header for every packet-socket type. > > There are some subtle points with variable length L2 protocols that > need to be reviewed. Come to think of it, if __dev_queue_xmit can unconditionally reset the mac header, then so can other tx paths. > > Reset the MAC header unconditionally so it is anchored for all of them, > > fixing the class at the source rather than hardening each consumer. > > > > The protocol probe is unchanged. A CONFIG_DEBUG_NET build stops warning > > about an unset mac header in skb_mac_header() on these paths, and the > > out-of-bounds eth_hdr() read no longer occurs. > > > > Found by 0sec (https://0sec.ai) using automated source analysis; > > verified against source and matched to the macsec KASAN report in > > f5089008f90c. Compile-tested. > > > > Fixes: 75c65772c3d1 ("net/packet: Ask driver for protocol if not provided by user") > > Cc: stable@vger.kernel.org > > Assisted-by: 0sec:multi-model > > Signed-off-by: Doruk Tan Ozturk > > --- > > This supersedes the per-consumer series "[PATCH net 0/3] net: dont read > > an unset MAC header on the raw/qdisc-bypass TX path" > > (https://lore.kernel.org/netdev/20260713194010.54642-1-doruk@0sec.ai/), > > per Jakubs suggestion to fix the problem at the source rather than > > hardening each driver. Vladimir Oltean had reviewed 2/3 of that series; > > this is a different (source) fix, so I have not carried the tags. > > net/packet/af_packet.c | 16 +++++++++++++--- > > 1 file changed, 13 insertions(+), 3 deletions(-) > > > > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > > index e75d2932475a..adfb9c19a3ca 100644 > > --- a/net/packet/af_packet.c > > +++ b/net/packet/af_packet.c > > @@ -1924,11 +1924,21 @@ static void packet_parse_headers(struct sk_buff *skb, struct socket *sock) > > { > > int depth; > > > > + /* > > + * packet_parse_headers() runs only on the transmit path > > + * (packet_sendmsg_spkt(), tpacket_fill_skb(), packet_snd()), where > > + * skb->data is the start of the L2 header for every packet-socket > > + * type: SOCK_RAW and SOCK_PACKET carry a user-supplied header and > > + * SOCK_DGRAM has one built by dev_hard_header(). Anchor the MAC > > + * header for all of them so a frame does not reach ndo_start_xmit() > > + * with the MAC header unset, where a driver reading eth_hdr(skb) on > > + * TX would dereference an out-of-bounds offset (skb->head + (u16)~0). > > + */ > > This is too verbose. Better captured in the commit message. > > > + skb_reset_mac_header(skb); > > + > > if ((!skb->protocol || skb->protocol == htons(ETH_P_ALL)) && > > - sock->type == SOCK_RAW) { > > - skb_reset_mac_header(skb); > > + sock->type == SOCK_RAW) > > skb->protocol = dev_parse_header_protocol(skb); > > - } > > > > /* Move network header to the right position for VLAN tagged packets */ > > if (likely(skb->dev->type == ARPHRD_ETHER) && > > -- > > 2.43.0 > > > >