[Bug 285650] The address of a CARP BACKUP node can be used as the source of outgoing packets

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=285650

            Bug ID: 285650
           Summary: The address of a CARP BACKUP node can be used as the
                    source of outgoing packets
           Product: Base System
           Version: 14.2-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: fault.seg@laposte.net

Hello all, it seems that, even after the commit
https://cgit.freebsd.org/src/commit/?id=d6e1ae659b11a13a9c289424735394173907c1d3,
the IP address of a CARP BACKUP node can still be used as the source of
outgoing packets.
This only occurs:
- after a down/up of the corresponding interface
- and the VIP address is the first declared alias for the corresponding network


Steps to reproduce:

Deploy two CARP nodes on FreeBSD 14.2-RELEASE (reproduced also on 13.3):

- Node 1: 
ifconfig_vmx2_alias0="inet 10.0.0.10 netmask 255.255.0.0 alias vhid 111 advskew
200 pass test"
ifconfig_vmx2_alias1="inet 10.0.0.1 netmask 255.255.0.0"
- Node 2:
ifconfig_vmx2_alias0="inet 10.0.0.10 netmask 255.255.0.0 alias vhid 111 advskew
200 pass test"
ifconfig_vmx2_alias1="inet 10.0.0.2 netmask 255.255.0.0"

On the BACKUP node:

- Outgoing packets to 10.0.0.0/16 use the correct local source address
- Restart the interface:
# ifconfig vmx2 down
kernel: carp: 111@vmx2: BACKUP -> INIT (hardware interface down)
kernel: carp: demoted by 240 to 480 (interface down)
# ifconfig vmx2 up
kernel: carp: 111@vmx2: INIT -> BACKUP (initialization complete)
kernel: carp: demoted by -240 to 240 (interface up)
- Outgoing packets to 10.0.0.0/16 now use the first declared IP address, which
is the CARP address in this case (in BACKUP state)

Any help to point out the cause of this unexpected behavior would be greatly
appreciated.

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