possible use-after-free in drivers/mtd/ubi/wl.c: erase_worker

[Emese Revfy]

Hi,

I think I found a potential problem in drivers/mtd/ubi/wl.c in
erase_worker():

1050         ubi_err("failed to erase PEB %d, error %d", pnum, err);
1051         kfree(wl_wrk);
1052         kmem_cache_free(ubi_wl_entry_slab, e);
1053
1054         if (err == -EINTR || err == -ENOMEM || err == -EAGAIN ||
1055             err == -EBUSY) {
1056                 int err1;
1057
1058                 /* Re-schedule the LEB for erasure */
1059                 err1 = schedule_erase(ubi, e, 0);

The pointer e is freed at line 1052 (kmem_cache_free), but
later it is passed to schedule_erase which will eventually call
erase_worker where it will be dereferenced and/or freed again.

It seems to have been introduced in commit
784c145444e7dd58ae740d406155b72ac658f151

Emese
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