dm verity fec: fix bufio leaks

Buffers read through dm_bufio_read() were not released in all code paths.

Fixes: a739ff3f ("dm verity: add support for forward error correction")
Cc: stable@vger.kernel.org # v4.5+
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-verity-fec.c

@@ -146,8 +146,6 @@ static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio,
 		block = fec_buffer_rs_block(v, fio, n, i);
 		res = fec_decode_rs8(v, fio, block, &par[offset], neras);
 		if (res < 0) {
-			dm_bufio_release(buf);
-
 			r = res;
 			goto error;
 		}
@@ -172,6 +170,8 @@ static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio,
 done:
 	r = corrected;
 error:
+	dm_bufio_release(buf);
+
 	if (r < 0 && neras)
 		DMERR_LIMIT("%s: FEC %llu: failed to correct: %d",
 			    v->data_dev->name, (unsigned long long)rsb, r);
@@ -269,7 +269,7 @@ static int fec_read_bufs(struct dm_verity *v, struct dm_verity_io *io,
 					  &is_zero) == 0) {
 			/* skip known zero blocks entirely */
 			if (is_zero)
-				continue;
+				goto done;
 
 			/*
 			 * skip if we have already found the theoretical