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 1312E357D0A; Sat, 17 Oct 2026 17:16:49 +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=1792257411; cv=none; b=AzFTElOPNA0kA04pGGu86i4VGjtxueODVht6EjSG3fmH3ylxJ8/4Pm1R2f+Le3hCFtFRopXyk3Xjo5UHRsh46ADxmj7GuAnhtc4U93AixOk1cHSKRk+EsP9D9/ekCtMslJPi3nH/6h6b7hl0LbPR2POPFTNXdcDEdpTtlQKQP08= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792257411; c=relaxed/simple; bh=rbzaHqdfu8ipyNWoTBDe41z+zpeIGSf8Yt/8I58hpE0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=LH+qlS7+BS6FTztoUDA4UQdrlgww4JOsatzLVz5oyu64ca/h3/tIrxvpTA71YgpCi2dnQB6xMNqm8JBnLQCYqN2BD6RKpJ0ZFJBYunMtPS9G8i0lcUv4isDWWnGFBS8apWbZ2NqByxA26sC3nrYMxTT14GcLljyvD9DIjzIFTOE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=cbry/UNX; 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="cbry/UNX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F6EC1F000C4; Sat, 17 Oct 2026 17:16:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1792257409; bh=RoAzhtVZDW+bWALz0GR9lqBGH/zLP53QRcS+XoepHHQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=cbry/UNX9mErb029XazTUj008n1binLHadJgGKoYxnBBJwheup/eiJ/zKa/s4yM+U 6VyI9UdFcwiAhmNkObBBcJmPyFqtXiRfBJcsLybZp/g8qmvsmIjLSBd/ZtLZNQ+cwO WBA2X35FH4+yioE3HUsLKxsc7pDWkCHIhJ97y8Ac= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Eric Dumazet , Willem de Bruijn , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.6 0550/1674] flow_dissector: avoid u16 truncation of skb->len when computing thoff Date: Sat, 17 Oct 2026 17:47:02 +0200 Message-ID: <20261017160445.213869799@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261017160431.119607952@linuxfoundation.org> References: <20261017160431.119607952@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: Eric Dumazet [ Upstream commit 99bda1ecbd56905f8bd934b9cdccd3bd251192b1 ] __skb_flow_dissect() computes key_control->thoff using: key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen); min_t(u16, ...) casts both arguments to u16 before comparing them. Whenever skb->len (or hlen) modulo 65536 is smaller than nhoff, the truncated length wins and thoff is set to a bogus small value, even when the dissection succeeded. For example, an IPv4/TCP frame with skb->len == 65540 and nhoff == 34 gets thoff == 4, so callers such as skb_probe_transport_header() point the transport header inside the Ethernet header. Such skbs are not exotic: - At the time of commit d0c081b49137 ("flow_dissector: properly cap thoff field"), AF_PACKET with PACKET_VNET_HDR could already build GSO skbs larger than 64KB (MTU checks are skipped for GSO, and alloc_skb_with_frags() accepted up to MAX_SKB_FRAGS (17) order-0 pages on top of the linear part). - BIG TCP now makes skbs larger than 64KB common. - The following patch makes tun_get_user() dissect IFF_TAP frames before eth_type_trans() pulls the Ethernet header, so a GSO frame carrying a 65522..65535 byte L3 packet will be dissected with skb->len in [65536, 65549]. Compare as u32 instead. If the resulting offset cannot be represented in the u16 key_control->thoff, cap it to U16_MAX and report the dissection as failed rather than silently returning a wrong transport offset. thoff is still set on failure, as some callers (such as eth_get_headlen()) use it regardless of the return value. Fixes: d0c081b49137 ("flow_dissector: properly cap thoff field") Signed-off-by: Eric Dumazet Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20261001191140.2818991-2-edumazet@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/core/flow_dissector.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index 00364d07ff6b1..37864578e8687 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -1047,6 +1047,7 @@ bool __skb_flow_dissect(const struct net *net, int mpls_lse = 0; int num_hdrs = 0; u8 ip_proto = 0; + u32 thoff; bool ret; if (!data) { @@ -1668,7 +1669,13 @@ bool __skb_flow_dissect(const struct net *net, ret = true; out: - key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen); + thoff = min_t(u32, nhoff, skb ? skb->len : hlen); + if (unlikely(thoff > U16_MAX)) { + /* Cannot be represented in key_control->thoff. */ + thoff = U16_MAX; + ret = false; + } + key_control->thoff = thoff; key_basic->n_proto = proto; key_basic->ip_proto = ip_proto; -- 2.53.0