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Thu, 1 Oct 2026 11:21:15 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 3MivFCtCvmqoJAAAD6G6ig (envelope-from ); Thu, 01 Oct 2026 11:21:15 +0000 Message-ID: <7590af05-e95a-4b34-9216-26e770bdfaaa@suse.de> Date: Thu, 1 Oct 2026 13:20:09 +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: Ilya Maximets , 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, echaudro@redhat.com, aconole@redhat.com, syzbot+4cc63fcfb3845e149969@syzkaller.appspotmail.com References: <20261001085205.3822-1-fmancera@suse.de> <50b0db80-7d42-44fc-81eb-d0fed8047871@ovn.org> Content-Language: en-US From: Fernando Fernandez Mancera In-Reply-To: <50b0db80-7d42-44fc-81eb-d0fed8047871@ovn.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; TAGGED_RCPT(0.00)[4cc63fcfb3845e149969]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[13]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[syzkaller.appspot.com:url,suse.de:mid,suse.de:email,imap1.dmz-prg2.suse.org:helo,appspotmail.com:email] X-Spam-Score: -2.80 X-Spam-Level: X-Spam-Flag: NO On 10/1/26 1:15 PM, Ilya Maximets wrote: > 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(). > Oh, I didn't notice that. In that case, this is harmless. I will update the commit message, thanks! >> 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. > Will do that. Thanks Ilya. > Best regards, Ilya Maximets.