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i.maximets@ovn.org, smtp.forwardemail.net, 149.28.215.223 X-Forward-Email-Version: 2.18.3 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: <360cc518-22f3-4afd-b62b-21c1d7b2ba87@ovn.org> Date: Thu, 8 Oct 2026 13:38:36 +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 v3] net: openvswitch: validate transport header presence in set_ipv6_addr To: Fernando Fernandez Mancera , netdev@vger.kernel.org Cc: dev@openvswitch.org, 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: <20261008104135.4722-1-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 10/8/26 12:41 PM, Fernando Fernandez Mancera wrote: > When executing IPv6 address rewrite actions on IPv6 fragments, > set_ipv6_addr() calls update_ipv6_checksum(). If parse_ipv6hdr() > processes a non-first IPv6 fragment, it sets key->ip.proto to > NEXTHDR_FRAGMENT and returns early without calling > skb_set_transport_header(). > > update_ipv6_checksum() unconditionally evaluates skb_transport_offset() > on entry before checking l4_proto. Because skb->transport_header is > uninitialized, this triggers a warning under CONFIG_DEBUG_NET=y although > it is completely harmless. > > Fix this by returning early in update_ipv6_checksum() if l4_proto is > NEXTHDR_FRAGMENT. This avoids reading the uninitialized transport offset > for fragments while preserving the debug warning for any other protocol > where the transport header is unexpectedly missing. > > 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 > --- > v3: drop the redundant comment introduced in v2 > --- > net/openvswitch/actions.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c > index dc5ff859f114..27152bca8a8c 100644 > --- a/net/openvswitch/actions.c > +++ b/net/openvswitch/actions.c > @@ -358,7 +358,12 @@ static void set_ip_addr(struct sk_buff *skb, struct iphdr *nh, > static void update_ipv6_checksum(struct sk_buff *skb, u8 l4_proto, > __be32 addr[4], const __be32 new_addr[4]) > { > - int transport_len = skb->len - skb_transport_offset(skb); > + int transport_len; > + > + if (l4_proto == NEXTHDR_FRAGMENT) > + return; > + > + transport_len = skb->len - skb_transport_offset(skb); > > if (l4_proto == NEXTHDR_TCP) { > if (likely(transport_len >= sizeof(struct tcphdr))) Thanks! Reviewed-by: Ilya Maximets