Patch "ubi: Fix UAF wear-leveling entry in eraseblk_count_seq_show()" has been added to the 4.19-stable tree

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This is a note to let you know that I've just added the patch titled

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

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ubi-fix-uaf-wear-leveling-entry-in-eraseblk_count_se.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ab1fd03e7b11449cf0c62f91a08faf26c4caae2f
Author: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
Date:   Sat Jul 30 19:28:37 2022 +0800

    ubi: Fix UAF wear-leveling entry in eraseblk_count_seq_show()
    
    [ Upstream commit a240bc5c43130c6aa50831d7caaa02a1d84e1bce ]
    
    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@xxxxxxxxxx>
    Signed-off-by: Richard Weinberger <richard@xxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index ac336164f6253..f1142a2d8bd22 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -865,8 +865,11 @@ 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;
 	}
 
@@ -1096,14 +1099,18 @@ 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



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