tree 2fc2d2322c5c44e0baa3726a3070caed8886a0a8
parent 5c8fe583cce542aa0b84adc939ce85293de36e5e
author Eric W. Biederman <ebiederm@xmission.com> 1608219720 -0600
committer Eric W. Biederman <ebiederm@xmission.com> 1609255955 -0600

capabilities: Don't allow writing ambiguous v3 file capabilities

The v3 file capabilities have a uid field that records the filesystem
uid of the root user of the user namespace the file capabilities are
valid in.

When someone is silly enough to have the same underlying uid as the
root uid of multiple nested containers a v3 filesystem capability can
be ambiguous.

In the spirit of don't do that then, forbid writing a v3 filesystem
capability if it is ambiguous.

Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities")
Reviewed-by: Andrew G. Morgan <morgan@kernel.org>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>