Docker: jail: name cannot be numeric fix

[Mateusz Guzik]

On Tue, Oct 27, 2015 at 05:19:26PM +0300, Sergey Zakharchenko wrote:
> Hello,
> 
> This is just a quick note that the problem mentioned in the Docker
> wiki https://wiki.freebsd.org/Docker :
> 
> > {{{
> > docker run -t -i centos /bin/bash
> > jail: name cannot be numeric (unless it is the jid
> > }}}
> >
> > Unknown: Noticed when re-running a container.
> 
> is not of an 'unknown' origin: it lies in sys/kern/kern_jail.c 's
> detection of numeric JIDs, which dates back to 2009:
> 
> https://svnweb.freebsd.org/base/head/sys/kern/kern_jail.c?revision=285685&view=markup
> 
> else if (*namelc == '0' || (strtoul(namelc, &p, 10) != jid && *p == '\0')))
> 
> It thinks everything that starts with a '0' is numeric, and doesn't
> check that it's the only character, e.g. namelc[1] == '\0'. This check
> is incorrect for some of the hex jail names that Docker generates.
> This is demonstrated by e.g. the following:
> 
>  ---> Running in 062a4f391fd9
> jail: name cannot be numeric (unless it is the jid)
> 
> Should I send a PR?
> 

What's the significance of said names?

The issue here is that said id may contain to letters, effectivley
looking like a number and that cannot be allowed due to jid/name
confusion.

While arbitrary names would be desirable, we are not going to get them
without some weird effort. As such, the right fix would e.g. prefix all
names with a letter and/or re-generated a name if it does not contain
any non-numeric characters.

The bogus check with 0 is only a side issue, which may or may not make
sense to be addressed.

-- 
Mateusz Guzik <mjguzik gmail.com>