tun: VIMAGE fix for if_tun cloner

[kp]

Summary

tun: VIMAGE fix for if_tun cloner

The if_tun cloner is not virtualised, but if_clone_attach() does use a
virtualised list of cloners.
The result is that we can't find the if_tun cloner when we try to remove
a renamed tun interface. Virtualise the cloner, and move the final
cleanup into a sysuninit so that we're sure this happens after all of
the vnet_sysuninits

Note that we need unit numbers to be system-unique (rather than unique
per vnet, as is done by if_clone_simple()). The unit number is used to
create the corresponding /dev/tunX device node, and this node must match
with the interface.
Switch to if_clone_advanced() so that we have control over the unit
numbers.

Reproduction scenario:
        jail -c -n foo persist vnet
        jexec test ifconfig tun create
        jexec test ifconfig tun0 name wg0
        jexec test ifconfig wg0 destroy

PR:     235704

[• hselasky]

Note that the character device subsystem is not virtualized, so tunX must be system uniq.

[kp]

Thanks. The original reporter of the bug discovered that too.

I'll see what I can do about that.

[kp]

Ensure that unit numbers are system-unique.

[kp]

Remove stray debug lines

[• hselasky]

sys/net/if_tun.c

182 ↗

(On Diff #54462)

Technically you should check there is a digit after tun?

if (name[0] == 't' && name[1] == 'u' && name[2] == 'n' && isdigit(name[3]))

[kp]

sys/net/if_tun.c

182 ↗

(On Diff #54462)

That'd break ifconfig tun create.

[• hselasky]

sys/net/if_tun.c

182 ↗

(On Diff #54462)

So check for (name[3] == 0 || isdigit(name[3]))

strncmp() will match anything that starts with tun.

[kp]

sys/net/if_tun.c

182 ↗

(On Diff #54462)

That is a good idea. I'll update the patch.

[kp]

Fix tun_clone_match() to not match on e.g. tunnel.

[hrs]

sys/net/if_tun.c

137 ↗

(On Diff #54462)

This should be VNET_DEFINE_STATIC() instead of VNET_DEFINE().

206 ↗

(On Diff #54462)

I think "%s%d", tunname, unit is better than a string literal "tun" here.

[kp]

Fix issues pointed out by hrs.

[kp]

If there are no objections I'm going to commit this soon.

[hrs]

Looks good to me.

[bz]

I hate manually virtualised cloners but people changed if_clone.c logic under the virtualised cloner infrastructure and I gave up on this years ago. Sorry I am not really helpful here currently. Also I think it needs more words describing the problem and part of the solution as I cannot imagine this only being a problem of tun(4) left but probably another few others?

sys/net/if_tun.c

184 ↗

(On Diff #54483)

Probably '\0'

[kp]

'\0'

[bz]

Thanks for updating the description; The repro scenario really should be a test case. Accept for the general idea, not for having checked the code in detail.