net: vxlan: prevent NULL deref in vxlan_xmit_one

net: vxlan: prevent NULL deref in vxlan_xmit_one

Neither sock4 nor sock6 pointers are guaranteed to be non-NULL in
vxlan_xmit_one, e.g. if the iface is brought down. This can lead to the
following NULL dereference:

  BUG: kernel NULL pointer dereference, address: 0000000000000010
  Oops: Oops: 0000 [#1] SMP NOPTI
  RIP: 0010:vxlan_xmit_one+0xbb3/0x1580
  Call Trace:
   vxlan_xmit+0x429/0x610
   dev_hard_start_xmit+0x55/0xa0
   __dev_queue_xmit+0x6d0/0x7f0
   ip_finish_output2+0x24b/0x590
   ip_output+0x63/0x110

Mentioned commits changed the code path in vxlan_xmit_one and as a side
effect the sock4/6 pointer validity checks in vxlan(6)_get_route were
lost. Fix this by adding back checks.

Since both commits being fixed were released in the same version (v6.7)
and are strongly related, bundle the fixes in a single commit.

Reported-by: Liang Li <liali@redhat.com>
Fixes: 6f19b2c136d9 ("vxlan: use generic function for tunnel IPv4 route lookup")
Fixes: 2aceb896ee18 ("vxlan: use generic function for tunnel IPv6 route lookup")
Cc: Beniamino Galvani <b.galvani@gmail.com>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20251126102627.74223-1-atenart@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>