ubi: Fix an error pointer dereference in error handling code

If "seen_pebs = init_seen(ubi);" fails then "seen_pebs" is an error pointer
and we try to kfree() it which results in an Oops.

This patch re-arranges the error handling so now it only frees things
which have been allocated successfully.

Fixes: daef3dd1 ("UBI: Fastmap: Add self check to detect absent PEBs")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/fastmap.c

@@ -1137,7 +1137,7 @@ static int ubi_write_fastmap(struct ubi_device *ubi,
 	struct rb_node *tmp_rb;
 	int ret, i, j, free_peb_count, used_peb_count, vol_count;
 	int scrub_peb_count, erase_peb_count;
-	unsigned long *seen_pebs = NULL;
+	unsigned long *seen_pebs;
 
 	fm_raw = ubi->fm_buf;
 	memset(ubi->fm_buf, 0, ubi->fm_size);
@@ -1151,7 +1151,7 @@ static int ubi_write_fastmap(struct ubi_device *ubi,
 	dvbuf = new_fm_vbuf(ubi, UBI_FM_DATA_VOLUME_ID);
 	if (!dvbuf) {
 		ret = -ENOMEM;
-		goto out_kfree;
+		goto out_free_avbuf;
 	}
 
 	avhdr = ubi_get_vid_hdr(avbuf);
@@ -1160,7 +1160,7 @@ static int ubi_write_fastmap(struct ubi_device *ubi,
 	seen_pebs = init_seen(ubi);
 	if (IS_ERR(seen_pebs)) {
 		ret = PTR_ERR(seen_pebs);
-		goto out_kfree;
+		goto out_free_dvbuf;
 	}
 
 	spin_lock(&ubi->volumes_lock);
@@ -1328,7 +1328,7 @@ static int ubi_write_fastmap(struct ubi_device *ubi,
 	ret = ubi_io_write_vid_hdr(ubi, new_fm->e[0]->pnum, avbuf);
 	if (ret) {
 		ubi_err(ubi, "unable to write vid_hdr to fastmap SB!");
-		goto out_kfree;
+		goto out_free_seen;
 	}
 
 	for (i = 0; i < new_fm->used_blocks; i++) {
@@ -1350,7 +1350,7 @@ static int ubi_write_fastmap(struct ubi_device *ubi,
 		if (ret) {
 			ubi_err(ubi, "unable to write vid_hdr to PEB %i!",
 				new_fm->e[i]->pnum);
-			goto out_kfree;
+			goto out_free_seen;
 		}
 	}
 
@@ -1360,7 +1360,7 @@ static int ubi_write_fastmap(struct ubi_device *ubi,
 		if (ret) {
 			ubi_err(ubi, "unable to write fastmap to PEB %i!",
 				new_fm->e[i]->pnum);
-			goto out_kfree;
+			goto out_free_seen;
 		}
 	}
 
@@ -1370,10 +1370,13 @@ static int ubi_write_fastmap(struct ubi_device *ubi,
 	ret = self_check_seen(ubi, seen_pebs);
 	dbg_bld("fastmap written!");
 
-out_kfree:
-	ubi_free_vid_buf(avbuf);
-	ubi_free_vid_buf(dvbuf);
+out_free_seen:
 	free_seen(seen_pebs);
+out_free_dvbuf:
+	ubi_free_vid_buf(dvbuf);
+out_free_avbuf:
+	ubi_free_vid_buf(avbuf);
+
 out:
 	return ret;
 }