CVE-2025-37921

In the Linux kernel, the following vulnerability has been resolved:

vxlan: vnifilter: Fix unlocked deletion of default FDB entry

When a VNI is deleted from a VXLAN device in 'vnifilter' mode, the FDB

entry associated with the default remote (assuming one was configured)

is deleted without holding the hash lock. This is wrong and will result

in a warning [1] being generated by the lockdep annotation that was

added by commit ebe642067455 ("vxlan: Create wrappers for FDB lookup").

Reproducer:

# ip link add vx0 up type vxlan dstport 4789 external vnifilter local 192.0.2.1

# bridge vni add vni 10010 remote 198.51.100.1 dev vx0

# bridge vni del vni 10010 dev vx0

Fix by acquiring the hash lock before the deletion and releasing it

afterwards. Blame the original commit that introduced the issue rather

than the one that exposed it.

[1]

WARNING: CPU: 3 PID: 392 at drivers/net/vxlan/vxlan_core.c:417 vxlan_find_mac+0x17f/0x1a0

[...]

RIP: 0010:vxlan_find_mac+0x17f/0x1a0

[...]

Call Trace:

<TASK>

__vxlan_fdb_delete+0xbe/0x560

vxlan_vni_delete_group+0x2ba/0x940

vxlan_vni_del.isra.0+0x15f/0x580

vxlan_process_vni_filter+0x38b/0x7b0

vxlan_vnifilter_process+0x3bb/0x510

rtnetlink_rcv_msg+0x2f7/0xb70

netlink_rcv_skb+0x131/0x360

netlink_unicast+0x426/0x710

netlink_sendmsg+0x75a/0xc20

__sock_sendmsg+0xc1/0x150

____sys_sendmsg+0x5aa/0x7b0

___sys_sendmsg+0xfc/0x180

__sys_sendmsg+0x121/0x1b0

do_syscall_64+0xbb/0x1d0

entry_SYSCALL_64_after_hwframe+0x4b/0x53