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_getdeviceinfo(struct xdr_stream *xdr,
				struct pnfs_device *pdev)
{
	__be32 *p;
	uint32_t len, type;
	int status;

	status = decode_op_hdr(xdr, OP_GETDEVICEINFO);
	if (status) {
		if (status == -ETOOSMALL) {
			p = xdr_inline_decode(xdr, 4);
			if (unlikely(!p))
				goto out_overflow;
			pdev->mincount = be32_to_cpup(p);
			dprintk("%s: Min count too small. mincnt = %u\n",
				__func__, pdev->mincount);
		}
		return status;
	}

	p = xdr_inline_decode(xdr, 8);
	if (unlikely(!p))
		goto out_overflow;
	type = be32_to_cpup(p++);
	if (type != pdev->layout_type) {
		dprintk("%s: layout mismatch req: %u pdev: %u\n",
			__func__, pdev->layout_type, type);
		return -EINVAL;
	}
	/*
	 * Get the length of the opaque device_addr4. xdr_read_pages places
	 * the opaque device_addr4 in the xdr_buf->pages (pnfs_device->pages)
	 * and places the remaining xdr data in xdr_buf->tail
	 */
	pdev->mincount = be32_to_cpup(p);
	xdr_read_pages(xdr, pdev->mincount); /* include space for the length */

	/* Parse notification bitmap, verifying that it is zero. */
	p = xdr_inline_decode(xdr, 4);
	if (unlikely(!p))
		goto out_overflow;
	len = be32_to_cpup(p);
	if (len) {
		uint32_t i;

		p = xdr_inline_decode(xdr, 4 * len);
		if (unlikely(!p))
			goto out_overflow;
		for (i = 0; i < len; i++, p++) {
			if (be32_to_cpup(p)) {
				dprintk("%s: notifications not supported\n",
					__func__);
				return -EIO;
			}
		}
	}
	return 0;
out_overflow:
	print_overflow_msg(__func__, xdr);
	return -EIO;
}

static int decode_getdeviceinfo(struct xdr_stream *xdr,
				struct pnfs_device *pdev)
{
	__be32 *p;
	uint32_t len, type;
	int status;

	status = decode_op_hdr(xdr, OP_GETDEVICEINFO);
	if (status) {
		if (status == -ETOOSMALL) {
			p = xdr_inline_decode(xdr, 4);
			if (unlikely(!p))
				goto out_overflow;
			pdev->mincount = be32_to_cpup(p);
			dprintk("%s: Min count too small. mincnt = %u\n",
				__func__, pdev->mincount);
		}
		return status;
	}

	p = xdr_inline_decode(xdr, 8);
	if (unlikely(!p))
		goto out_overflow;
	type = be32_to_cpup(p++);
	if (type != pdev->layout_type) {
		dprintk("%s: layout mismatch req: %u pdev: %u\n",
			__func__, pdev->layout_type, type);
		return -EINVAL;
	}
	/*
	 * Get the length of the opaque device_addr4. xdr_read_pages places
	 * the opaque device_addr4 in the xdr_buf->pages (pnfs_device->pages)
	 * and places the remaining xdr data in xdr_buf->tail
	 */
	pdev->mincount = be32_to_cpup(p);
	xdr_read_pages(xdr, pdev->mincount); /* include space for the length */

	/* Parse notification bitmap, verifying that it is zero. */
	p = xdr_inline_decode(xdr, 4);
	if (unlikely(!p))
		goto out_overflow;
	len = be32_to_cpup(p);
	if (len) {
		uint32_t i;

		p = xdr_inline_decode(xdr, 4 * len);
		if (unlikely(!p))
			goto out_overflow;
		for (i = 0; i < len; i++, p++) {
			if (be32_to_cpup(p)) {
				dprintk("%s: notifications not supported\n",
					__func__);
				return -EIO;
			}
		}
	}
	return 0;
out_overflow:
	print_overflow_msg(__func__, xdr);
	return -EIO;
}
