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 5EFF63DA5D6; Tue, 25 Aug 2026 14:00:32 +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=1787666433; cv=none; b=ndbUgljbUFnSznCBHa37+88LmgmXwWgPJxYL2MiLZigzZN7zfwIxjhWg/bubwkyeiQFz7dyBBDWpVO/T4bqanSkS814b0WOveB/FbMOqNtvFIyHWvP5N1Lo3otM2BVcP+m5MC/5GY+O3b953/HrRWiCMme/vohPxSkgjBquX+q4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787666433; c=relaxed/simple; bh=PC5GupBHBVXs6WJOhlemeW/RtNbx9g9LH+BrhEcThzg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jloUcPR4xxklr4ttvFa1a1gcK04ryvS8JZVt4LtKpQ5PBhemVitEqQ3MVMwIloPinjYW0wcPkYrPxgPUZlzvUjDit8p8GwuJJzZxna4c55c58AwMTJ9yeBn/jx1evJ0NdKlkrH9K5+DanqDRangrq8dnA14gECeDB+8O/WbyUio= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Hw/2FAwu; 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="Hw/2FAwu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9E0D81F00A3D; Tue, 25 Aug 2026 14:00:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1787666432; bh=g9WVyA58/aXeMikP9uGJU66AQ13jjf3+dBGo8KHgMGo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Hw/2FAwuuVzeTDuc/OY6S0WDsEzm2DpfvWoBkVpvxIX6myOA7w6TNOWAaNameb6AK gE8curps9YhYMMOcGQZTstnH4kJOTU/l0b/ulquRXFXSfIo7b/rsZ5+WpSIUVPyOER HNoF0qtbF13TZ+V5NZC6hPCgz6nImL09T0ARe8rQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Vega , Yong Wang , Ren Wei , Ido Schimmel , Jakub Kicinski Subject: [PATCH 5.10 40/57] ipv4: reject undersized MTUs in ip_do_fragment() Date: Tue, 25 Aug 2026 15:27:02 +0200 Message-ID: <20260825132542.896066326@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260825132541.342390421@linuxfoundation.org> References: <20260825132541.342390421@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 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yong Wang commit c0726f0caf8c6b3208552949e17d23634a2f3129 upstream. ip_do_fragment() subtracts the IPv4 header length from the effective MTU and passes the resulting payload MTU to ip_frag_next(). If the effective MTU is smaller than hlen + 8, ip_frag_next() rounds the fragment payload length down to zero. The fragmentation state then never makes forward progress: state->left, state->ptr and state->offset stay unchanged while ip_do_fragment() keeps allocating and transmitting header-only fragments until the softlockup detector fires. This is reproducible with a route installed using "mtu lock 20", but it is also reproducible without route MTU lock, for example by forwarding a packet to a device whose MTU is 20. Fix it in ip_do_fragment() by rejecting mtu < hlen + 8 with -EMSGSIZE, matching the existing IPv6 fragmentation check. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Reported-by: Vega Signed-off-by: Yong Wang Signed-off-by: Ren Wei Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/8809ef6314b98913681b0b370a05a85c2b6cd579.1786599079.git.edragain@163.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/ipv4/ip_output.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/net/ipv4/ip_output.c +++ b/net/ipv4/ip_output.c @@ -798,6 +798,10 @@ int ip_do_fragment(struct net *net, stru */ hlen = iph->ihl * 4; + if (mtu < hlen + 8) { + err = -EMSGSIZE; + goto fail; + } mtu = mtu - hlen; /* Size of data space */ IPCB(skb)->flags |= IPSKB_FRAG_COMPLETE; ll_rs = LL_RESERVED_SPACE(rt->dst.dev);