From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.forwardemail.net (smtp.forwardemail.net [121.127.44.66]) (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 54BDB46EC79 for ; Thu, 1 Oct 2026 11:17:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=121.127.44.66 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790853480; cv=none; b=aT2gi24F6onrsOLnvzA8C0lZGxHJoFO197om3lF8w5fEdnp+Z/TlSYob27nw7XEiZqBV1tJU/yy0rqOIsRK1ZibNNKe288zBZX7WBMxDW0SlhFVrIcxHh4NQwGS8ngVxITgQvHnfXwUTGVZADrm72NH8SItGYqvhw3hkdqEZSSk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790853480; c=relaxed/simple; bh=U241GdGIVluRm8oGZBm41X5qru4sUD5Ky9XAbESWFz8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gxz5cDGT9udG+VfO9v7iaBoG9equjmRi1e+NB4GdAPEC1NRAniKH3pUgzswqMq5MFZrCZ2FjrA6tMDj0XCPzwpVxy5ny2xEDTqibBNx8RDIJ0KmZtPbT6nlROqcGjHznyt0acP1SNJRlTykw/h0Z0bYM/Fww1BS2KspEsM3Giv8= ARC-Authentication-Results:i=1; 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i.maximets@ovn.org, smtp.forwardemail.net, 121.127.44.66 X-Forward-Email-Version: 2.16.7 X-Forward-Email-Website: https://forwardemail.net X-Complaints-To: abuse@forwardemail.net X-Report-Abuse: abuse@forwardemail.net X-Report-Abuse-To: abuse@forwardemail.net Message-ID: <50b0db80-7d42-44fc-81eb-d0fed8047871@ovn.org> Date: Thu, 1 Oct 2026 13:15:21 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] net: openvswitch: validate transport header presence in set_ipv6_addr To: Fernando Fernandez Mancera , netdev@vger.kernel.org Cc: dev@openvswitch.org, aatteka@nicira.com, jesse@nicira.com, horms@kernel.org, pabeni@redhat.com, kuba@kernel.org, edumazet@kernel.org, davem@davemloft.net, i.maximets@ovn.org, echaudro@redhat.com, aconole@redhat.com, syzbot+4cc63fcfb3845e149969@syzkaller.appspotmail.com References: <20261001085205.3822-1-fmancera@suse.de> Content-Language: en-US From: Ilya Maximets Autocrypt: addr=i.maximets@ovn.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/1/26 10:52 AM, Fernando Fernandez Mancera wrote: > When executing IPv6 address rewrite actions on IPv6 fragments, > set_ipv6_addr() might attempt to recalculate the L4 header checksum > calling skb_transport_header() with an uninitialized transport header. > This can potentially lead to a OOB write. Not really. later fragments have l4_proto set to NEXTHDR_FRAGMENT and so no writes will be performed. See parse_ipv6hdr(). > A warning is triggered with DEBUG_NET=y. Yeah, while the value is not actually used to access the packet data, the skbuff core generates a warning on read. > > Fix this by recalculating the checksum only if there is a valid > transport header in the skb. Otherwise, assume this is a fragment and > skip it. > > See the syzbot trace: > > !skb_transport_header_was_set(skb) > WARNING: ./include/linux/skbuff.h:3075 at skb_transport_header include/linux/skbuff.h:3075 [inline], CPU#1: syz-executor463/5635 > WARNING: ./include/linux/skbuff.h:3075 at skb_transport_offset include/linux/skbuff.h:3250 [inline], CPU#1: syz-executor463/5635 > WARNING: ./include/linux/skbuff.h:3075 at update_ipv6_checksum net/openvswitch/actions.c:361 [inline], CPU#1: syz-executor463/5635 > WARNING: ./include/linux/skbuff.h:3075 at set_ipv6_addr+0x462/0x660 net/openvswitch/actions.c:399, CPU#1: syz-executor463/5635 > [...] > RIP: 0010:skb_transport_header include/linux/skbuff.h:3075 [inline] > RIP: 0010:skb_transport_offset include/linux/skbuff.h:3250 [inline] > RIP: 0010:update_ipv6_checksum net/openvswitch/actions.c:361 [inline] > RIP: 0010:set_ipv6_addr+0x462/0x660 net/openvswitch/actions.c:399 > [...] > Call Trace: > > set_ipv6 net/openvswitch/actions.c:531 [inline] > do_execute_actions+0x557e/0x8600 net/openvswitch/actions.c:1366 > ovs_execute_actions+0xde/0x520 net/openvswitch/actions.c:1592 > ovs_packet_cmd_execute+0xb4f/0xf10 net/openvswitch/datapath.c:705 > genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114 > genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209 > netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2572 > genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218 > netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1361 > netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1916 > sock_sendmsg_nosec+0x14e/0x190 net/socket.c:800 > > Reported-by: syzbot+4cc63fcfb3845e149969@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=4cc63fcfb3845e149969 > Fixes: 3fdbd1ce11e5 ("openvswitch: add ipv6 'set' action") > Signed-off-by: Fernando Fernandez Mancera > --- > net/openvswitch/actions.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c > index dc5ff859f114..a14668565ec4 100644 > --- a/net/openvswitch/actions.c > +++ b/net/openvswitch/actions.c > @@ -395,7 +395,7 @@ static void set_ipv6_addr(struct sk_buff *skb, u8 l4_proto, > __be32 addr[4], const __be32 new_addr[4], > bool recalculate_csum) > { > - if (recalculate_csum) > + if (recalculate_csum && skb_transport_header_was_set(skb)) > update_ipv6_checksum(skb, l4_proto, addr, new_addr); I'd suggest moving the check into update_ipv6_checksum() and maybe add a small comment that the check is only to avoid warning on reading the offset that wasn't set, offset must always be set for any l4_proto for which the checksum is actually getting updated. Best regards, Ilya Maximets.