tree 768e1d799f6d6a4a7f85f48d9e9fc431dc8d017c
parent 6c23cbbd5056b155401b0a2b5567d530e6c750c4
author Eric W. Biederman <ebiederm@xmission.com> 1363200709 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> 1363212020 -0700

userns: Don't allow CLONE_NEWUSER | CLONE_FS

Don't allowing sharing the root directory with processes in a
different user namespace.  There doesn't seem to be any point, and to
allow it would require the overhead of putting a user namespace
reference in fs_struct (for permission checks) and incrementing that
reference count on practically every call to fork.

So just perform the inexpensive test of forbidding sharing fs_struct
acrosss processes in different user namespaces.  We already disallow
other forms of threading when unsharing a user namespace so this
should be no real burden in practice.

This updates setns, clone, and unshare to disallow multiple user
namespaces sharing an fs_struct.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>