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 7882031353C; Tue, 13 Oct 2026 12:30:06 +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=1791894607; cv=none; b=B/fA3LWYo680YD8adQmTrytVpRfkZUqBoNao4hNXf/TearZMP3Talnr3ooZEfssenSGBAwgIp1BUSDodjxrfjxL92Ok7IsfVaxRD8O7MDn9smtsUhuFuiBnUIhJHs6Wtqn0YnuP1aus9CE5b8joYu4r6X6oh/4m9qPVEjI1sIBw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791894607; c=relaxed/simple; bh=ypcOqb7HpkBdpJHHzH73LKwAahVm7M4VOqk0JSmzvK8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=EnX9dKWdrwZtRvAR3ZoNgbcDiU/oghoIfgIhIqfQEDVkrlZB7K+WjbDbMPp7n48s3oVupvXwS9h2OVkwpvjs/xPOMWocGb0TcI1T8fOj2DwHA/+oD7bY7D/09Q7kVdjrogQJiGvi75QOK0iaVu/z552gtW1IDaFf1DoeO+208Js= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=VkKmHP4c; 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="VkKmHP4c" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CECA51F00893; Tue, 13 Oct 2026 12:30:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791894606; bh=VarfkDE1m6uIwapMB+X3XpiFokRiLIbxbz8TEd1Bt08=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=VkKmHP4cTxbrFBEjAdui/IbQjjw+uikP0KC9g8vEmzAgsNJUF9v2fEwSlY0G3QlhH MmRgJX9KrPaHHqg9+FqVZOW+Fs9fcpL1jBXyfRoyh2l9Irs0TEx8nZh7E9FzAjWbdz mXCVPNIfqwvKt8itZ3ZnNtw5z7aeDOGApGPLWqLY= 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 6.18 580/621] flow_dissector: avoid u16 truncation of skb->len when computing thoff Date: Tue, 13 Oct 2026 13:39:35 +0200 Message-ID: <20261013112934.568823285@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261013112920.855194808@linuxfoundation.org> References: <20261013112920.855194808@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 6.18-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 8aa4f9b4df810..27d8a01bc9230 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -1071,6 +1071,7 @@ 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) { @@ -1692,7 +1693,13 @@ 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