NFSv4: include bitmap in nfsv4 get acl data

The NFSv4 bitmap size is unbounded: a server can return an arbitrary
sized bitmap in an FATTR4_WORD0_ACL request.  Replace using the
nfs4_fattr_bitmap_maxsz as a guess to the maximum bitmask returned by a server
with the inclusion of the bitmap (xdr length plus bitmasks) and the acl data
xdr length to the (cached) acl page data.

This is a general solution to commit e5012d1f "NFSv4.1: update
nfs4_fattr_bitmap_maxsz" and fixes hitting a BUG_ON in xdr_shrink_bufhead
when getting ACLs.

Fix a bug in decode_getacl that returned -EINVAL on ACLs > page when getxattr
was called with a NULL buffer, preventing ACL > PAGE_SIZE from being retrieved.

Cc: stable@kernel.org
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
static int decode_attr_maxfilesize(struct xdr_stream *xdr, uint32_t *bitmap, uint64_t *res)
{
	__be32 *p;
	int status = 0;

	*res = 0;
	if (unlikely(bitmap[0] & (FATTR4_WORD0_MAXFILESIZE - 1U)))
		return -EIO;
	if (likely(bitmap[0] & FATTR4_WORD0_MAXFILESIZE)) {
		p = xdr_inline_decode(xdr, 8);
		if (unlikely(!p))
			goto out_overflow;
		xdr_decode_hyper(p, res);
		bitmap[0] &= ~FATTR4_WORD0_MAXFILESIZE;
	}
	dprintk("%s: maxfilesize=%Lu\n", __func__, (unsigned long long)*res);
	return status;
out_overflow:
	print_overflow_msg(__func__, xdr);
	return -EIO;
}

static int decode_attr_maxfilesize(struct xdr_stream *xdr, uint32_t *bitmap, uint64_t *res)
{
	__be32 *p;
	int status = 0;

	*res = 0;
	if (unlikely(bitmap[0] & (FATTR4_WORD0_MAXFILESIZE - 1U)))
		return -EIO;
	if (likely(bitmap[0] & FATTR4_WORD0_MAXFILESIZE)) {
		p = xdr_inline_decode(xdr, 8);
		if (unlikely(!p))
			goto out_overflow;
		xdr_decode_hyper(p, res);
		bitmap[0] &= ~FATTR4_WORD0_MAXFILESIZE;
	}
	dprintk("%s: maxfilesize=%Lu\n", __func__, (unsigned long long)*res);
	return status;
out_overflow:
	print_overflow_msg(__func__, xdr);
	return -EIO;
}
