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: > <TASK> > 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: [email protected] > Closes: https://syzkaller.appspot.com/bug?extid=4cc63fcfb3845e149969 > Fixes: 3fdbd1ce11e5 ("openvswitch: add ipv6 'set' action") > Signed-off-by: Fernando Fernandez Mancera <[email protected]> > --- > 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. _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
