userns: Don't allow CLONE_NEWUSER | CLONE_FS

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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>

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This commit is contained in:

Eric W. Biederman 2013-03-13 11:51:49 -07:00 • committed by Linus Torvalds

parent 6c23cbbd50

commit e66eded830

2 changed files with 8 additions and 1 deletions

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5

kernel/fork.c

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4

kernel/user_namespace.c

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