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authorEric W. Biederman <ebiederm@xmission.com>2014-12-05 17:51:47 -0600
committerEric W. Biederman <ebiederm@xmission.com>2014-12-05 19:07:26 -0600
commit0542f17bf2c1f2430d368f44c8fcf2f82ec9e53e (patch)
treef52eba42635a23cb5c2b6a49eb3180285ccba925 /kernel/groups.c
parent7ff4d90b4c24a03666f296c3d4878cd39001e81e (diff)
userns: Document what the invariant required for safe unprivileged mappings.
The rule is simple. Don't allow anything that wouldn't be allowed without unprivileged mappings. It was previously overlooked that establishing gid mappings would allow dropping groups and potentially gaining permission to files and directories that had lesser permissions for a specific group than for all other users. This is the rule needed to fix CVE-2014-8989 and prevent any other security issues with new_idmap_permitted. The reason for this rule is that the unix permission model is old and there are programs out there somewhere that take advantage of every little corner of it. So allowing a uid or gid mapping to be established without privielge that would allow anything that would not be allowed without that mapping will result in expectations from some code somewhere being violated. Violated expectations about the behavior of the OS is a long way to say a security issue. Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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