Re: nsswitch: do not reload if "/" changes

[Carlos O'Donell via Libc-alpha <libc-alpha@sourceware.org>]

On 1/15/21 7:59 PM, DJ Delorie via Libc-alpha wrote:
> 
> [Note: I tried putting this functionality in the file_change_detection
> module, but that didn't have enough persistence.]
> 
> [Note: tested by instrumenting test-container.c and observing the
> instrumentation with test containers on the root fs and on a separate
> fs]
> 
> https://sourceware.org/bugzilla/show_bug.cgi?id=27077
> 
> Before reloading nsswitch.conf, verify that the root directory
> hasn't changed - if it has, it's likely that we've entered a
> container and should not trust the nsswitch inside the container
> nor load any shared objects therein.

Can we create a non-test-container test for this?

I think you can use support_become_root to unshare and then try
to use support_chroot_create/support_chroot_free and xhcroot to 
change root, and then try to do an NSS call that will fail?

The test can start by calling __nss_lookup_configure to set
a known module to provide the NSS values, and then do an IdM
call, verify you're using a known value, and then try to
become root and chroot.

I'm not sure if this is possible though.

-- 
Cheers,
Carlos.