Re: [PATCH 2/2] groups: Allow unprivileged processes to use setgroups to drop groups

Theodore Ts'o
2014-11-16T03:40:18Z

On Sat, Nov 15, 2014 at 06:35:05PM -0800, Josh Triplett wrote:
> >So arbitrarily anyone to drop groups from their supplemental group
> >list will result in a change from both existing practice and legacy
> >Unix systems, and it could potentially lead to a security exposure.
>
> As Andy pointed out, you can already do that with a user namespace,
> for any case not involving a setuid or setgid (or otherwise
> privilege-gaining) program. And requiring no_new_privs handles
> that.

Well, it's no worse than what we can do already with the user
namespace, yes. I'm still worried it's going to come as a surprise
for some configurations because it's a change from what was allowed
historically. Then again, pretty much all of the tripwire and rootkit
scanners won't notice a "setuid" program that uses capabilities
instead of the traditional setuid bit, and most sysadmins won't think
to check for an executable with a forced capability mask, so this
isn't exactly a new problem....

- Ted