• Eric W. Biederman's avatar
    userns: Don't allow CLONE_NEWUSER | CLONE_FS · e66eded8
    Eric W. Biederman authored
    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>
    e66eded8
user_namespace.c 22.2 KB