mtd: ubi: fixup error correction in do_sync_erase()

Since fastmap we gained do_sync_erase(). This function can return an error
and its error handling isn't obvious. First the memory allocation for
struct ubi_work can fail and as such struct ubi_wl_entry is leaked.
However if the memory allocation succeeds then the tail function takes
care of the struct ubi_wl_entry. A free here could result in a double
free.
To make the error handling simpler, I split the tail function into one
piece which does the work and another which frees the struct ubi_work
which is passed as argument. As result do_sync_erase() can keep the
struct on stack and we get rid of one error source.

Cc: <stable@vger.kernel.org>
Fixes: 8199b90 ("UBI: Add fastmap support to the WL sub-system")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/wl.c

@@ -603,6 +603,7 @@ static int schedule_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
 	return 0;
 }
 
+static int __erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk);
 /**
  * do_sync_erase - run the erase worker synchronously.
  * @ubi: UBI device description object
@@ -615,20 +616,16 @@ static int schedule_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
 static int do_sync_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
 			 int vol_id, int lnum, int torture)
 {
-	struct ubi_work *wl_wrk;
+	struct ubi_work wl_wrk;
 
 	dbg_wl("sync erase of PEB %i", e->pnum);
 
-	wl_wrk = kmalloc(sizeof(struct ubi_work), GFP_NOFS);
-	if (!wl_wrk)
-		return -ENOMEM;
-
-	wl_wrk->e = e;
-	wl_wrk->vol_id = vol_id;
-	wl_wrk->lnum = lnum;
-	wl_wrk->torture = torture;
+	wl_wrk.e = e;
+	wl_wrk.vol_id = vol_id;
+	wl_wrk.lnum = lnum;
+	wl_wrk.torture = torture;
 
-	return erase_worker(ubi, wl_wrk, 0);
+	return __erase_worker(ubi, &wl_wrk);
 }
 
 /**
@@ -1014,7 +1011,7 @@ static int ensure_wear_leveling(struct ubi_device *ubi, int nested)
 }
 
 /**
- * erase_worker - physical eraseblock erase worker function.
+ * __erase_worker - physical eraseblock erase worker function.
  * @ubi: UBI device description object
  * @wl_wrk: the work object
  * @shutdown: non-zero if the worker has to free memory and exit
@@ -1025,30 +1022,19 @@ static int ensure_wear_leveling(struct ubi_device *ubi, int nested)
  * needed. Returns zero in case of success and a negative error code in case of
  * failure.
  */
-static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
-			int shutdown)
+static int __erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk)
 {
 	struct ubi_wl_entry *e = wl_wrk->e;
 	int pnum = e->pnum;
 	int vol_id = wl_wrk->vol_id;
 	int lnum = wl_wrk->lnum;
 	int err, available_consumed = 0;
 
-	if (shutdown) {
-		dbg_wl("cancel erasure of PEB %d EC %d", pnum, e->ec);
-		kfree(wl_wrk);
-		wl_entry_destroy(ubi, e);
-		return 0;
-	}
-
 	dbg_wl("erase PEB %d EC %d LEB %d:%d",
 	       pnum, e->ec, wl_wrk->vol_id, wl_wrk->lnum);
 
 	err = sync_erase(ubi, e, wl_wrk->torture);
 	if (!err) {
-		/* Fine, we've erased it successfully */
-		kfree(wl_wrk);
-
 		spin_lock(&ubi->wl_lock);
 		wl_tree_add(e, &ubi->free);
 		ubi->free_count++;
@@ -1066,7 +1052,6 @@ static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
 	}
 
 	ubi_err(ubi, "failed to erase PEB %d, error %d", pnum, err);
-	kfree(wl_wrk);
 
 	if (err == -EINTR || err == -ENOMEM || err == -EAGAIN ||
 	    err == -EBUSY) {
@@ -1150,6 +1135,25 @@ static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
 	return err;
 }
 
+static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
+			  int shutdown)
+{
+	int ret;
+
+	if (shutdown) {
+		struct ubi_wl_entry *e = wl_wrk->e;
+
+		dbg_wl("cancel erasure of PEB %d EC %d", e->pnum, e->ec);
+		kfree(wl_wrk);
+		wl_entry_destroy(ubi, e);
+		return 0;
+	}
+
+	ret = __erase_worker(ubi, wl_wrk);
+	kfree(wl_wrk);
+	return ret;
+}
+
 /**
  * ubi_wl_put_peb - return a PEB to the wear-leveling sub-system.
  * @ubi: UBI device description object