nfsd: Fix error return values for nfsd4_clone_file_range()

If the parameter 'count' is non-zero, nfsd4_clone_file_range() will
currently clobber all errors returned by vfs_clone_file_range() and
replace them with EINVAL.

Fixes: 42ec3d4c ("vfs: make remap_file_range functions take and...")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: stable@vger.kernel.org # v4.20+
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/vfs.c

@@ -557,9 +557,11 @@ __be32 nfsd4_clone_file_range(struct file *src, u64 src_pos, struct file *dst,
 	loff_t cloned;
 
 	cloned = vfs_clone_file_range(src, src_pos, dst, dst_pos, count, 0);
+	if (cloned < 0)
+		return nfserrno(cloned);
 	if (count && cloned != count)
-		cloned = -EINVAL;
-	return nfserrno(cloned < 0 ? cloned : 0);
+		return nfserrno(-EINVAL);
+	return 0;
 }
 
 ssize_t nfsd_copy_file_range(struct file *src, u64 src_pos, struct file *dst,