ubi: Fix UAF wear-leveling entry in eraseblk_count_seq_show()

Wear-leveling entry could be freed in error path, which may be accessed
again in eraseblk_count_seq_show(), for example:

__erase_worker                eraseblk_count_seq_show
                                wl = ubi->lookuptbl[*block_number]
				if (wl)
  wl_entry_destroy
    ubi->lookuptbl[e->pnum] = NULL
    kmem_cache_free(ubi_wl_entry_slab, e)
		                   erase_count = wl->ec  // UAF!

Wear-leveling entry updating/accessing in ubi->lookuptbl should be
protected by ubi->wl_lock, fix it by adding ubi->wl_lock to serialize
wl entry accessing between wl_entry_destroy() and
eraseblk_count_seq_show().

Fetch a reproducer in [Link].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216305
Fixes: 7bccd12d27b7e3 ("ubi: Add debugfs file for tracking PEB state")
Fixes: 801c135ce73d5d ("UBI: Unsorted Block Images")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 68eb0f2..f45df3b 100644 (file)
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -890,8 +890,11 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 
        err = do_sync_erase(ubi, e1, vol_id, lnum, 0);
        if (err) {
-               if (e2)
+               if (e2) {
+                       spin_lock(&ubi->wl_lock);
                        wl_entry_destroy(ubi, e2);
+                       spin_unlock(&ubi->wl_lock);
+               }
                goto out_ro;
        }
 
@@ -1130,14 +1133,18 @@ static int __erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk)
                /* Re-schedule the LEB for erasure */
                err1 = schedule_erase(ubi, e, vol_id, lnum, 0, false);
                if (err1) {
+                       spin_lock(&ubi->wl_lock);
                        wl_entry_destroy(ubi, e);
+                       spin_unlock(&ubi->wl_lock);
                        err = err1;
                        goto out_ro;
                }
                return err;
        }
 
+       spin_lock(&ubi->wl_lock);
        wl_entry_destroy(ubi, e);
+       spin_unlock(&ubi->wl_lock);
        if (err != -EIO)
                /*
                 * If this is not %-EIO, we have no idea what to do. Scheduling