This basically audits the callers of xattr_permission(), which calls
permission() and can perform writes to the filesystem.

[AV: add missing parts - removexattr() and nfsd posix acls, plug for a leak
spotted by Miklos]
Acked-by: NAl Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDave Hansen <haveblue@us.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>