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_time_access(struct xdr_stream *xdr, uint32_t *bitmap, struct timespec *time)
{
	int status = 0;

	time->tv_sec = 0;
	time->tv_nsec = 0;
	if (unlikely(bitmap[1] & (FATTR4_WORD1_TIME_ACCESS - 1U)))
		return -EIO;
	if (likely(bitmap[1] & FATTR4_WORD1_TIME_ACCESS)) {
		status = decode_attr_time(xdr, time);
		if (status == 0)
			status = NFS_ATTR_FATTR_ATIME;
		bitmap[1] &= ~FATTR4_WORD1_TIME_ACCESS;
	}
	dprintk("%s: atime=%ld\n", __func__, (long)time->tv_sec);
	return status;
}

static int decode_attr_time_access(struct xdr_stream *xdr, uint32_t *bitmap, struct timespec *time)
{
	int status = 0;

	time->tv_sec = 0;
	time->tv_nsec = 0;
	if (unlikely(bitmap[1] & (FATTR4_WORD1_TIME_ACCESS - 1U)))
		return -EIO;
	if (likely(bitmap[1] & FATTR4_WORD1_TIME_ACCESS)) {
		status = decode_attr_time(xdr, time);
		if (status == 0)
			status = NFS_ATTR_FATTR_ATIME;
		bitmap[1] &= ~FATTR4_WORD1_TIME_ACCESS;
	}
	dprintk("%s: atime=%ld\n", __func__, (long)time->tv_sec);
	return status;
}
