Commit 3c6a4b11330f for kernel

commit 3c6a4b11330fe424557538a98fca9f0a4c5bf313
Author: Fernando Fernandez Mancera <fmancera@suse.de>
Date:   Thu Oct 8 12:41:35 2026 +0200

    net: openvswitch: validate transport header presence in set_ipv6_addr

    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:
     <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: 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 <fmancera@suse.de>
    Reviewed-by: Ilya Maximets <i.maximets@ovn.org>
    Link: https://patch.msgid.link/20261008104135.4722-1-fmancera@suse.de
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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)))