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Commit e66eded8 authored by Eric W. Biederman's avatar Eric W. Biederman Committed by Linus Torvalds
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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: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6c23cbbd
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