* Re: possible use-after-free in drivers/mtd/ubi/wl.c: erase_worker
2012-01-03 23:34 possible use-after-free in drivers/mtd/ubi/wl.c: erase_worker Emese Revfy
@ 2012-01-04 17:33 ` Josh Boyer
2012-01-05 9:14 ` Artem Bityutskiy
1 sibling, 0 replies; 3+ messages in thread
From: Josh Boyer @ 2012-01-04 17:33 UTC (permalink / raw)
To: Emese Revfy; +Cc: dedekind1, dwmw2, linux-mtd, linux-kernel
On Tue, Jan 3, 2012 at 6:34 PM, Emese Revfy <re.emese@gmail.com> wrote:
> 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.
Yes. That does seem to be a problem. Care to create a patch that solves this
by deferring the frees until after the err variable is checked?
josh
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: possible use-after-free in drivers/mtd/ubi/wl.c: erase_worker
2012-01-03 23:34 possible use-after-free in drivers/mtd/ubi/wl.c: erase_worker Emese Revfy
2012-01-04 17:33 ` Josh Boyer
@ 2012-01-05 9:14 ` Artem Bityutskiy
1 sibling, 0 replies; 3+ messages in thread
From: Artem Bityutskiy @ 2012-01-05 9:14 UTC (permalink / raw)
To: Emese Revfy; +Cc: dwmw2, linux-mtd, linux-kernel
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Well-spotted, thanks. I've just pushed this patch to the UBIFS git tree:
From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Subject: [PATCH] UBI: fix use-after-free on error path
When we fail to erase a PEB, we free the corresponding erase entry object,
but then re-schedule this object if the error code was something like -EAGAIN.
Obviously, it is a bug to use the object after we have freed it.
Reported-by: Emese Revfy <re.emese@gmail.com>
Cc: stable@kernel.org [v2.6.23+]
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
---
drivers/mtd/ubi/wl.c | 7 ++++---
1 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 42c684c..036d213 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -1049,7 +1049,6 @@ static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
ubi_err("failed to erase PEB %d, error %d", pnum, err);
kfree(wl_wrk);
- kmem_cache_free(ubi_wl_entry_slab, e);
if (err == -EINTR || err == -ENOMEM || err == -EAGAIN ||
err == -EBUSY) {
@@ -1062,14 +1061,16 @@ static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
goto out_ro;
}
return err;
- } else if (err != -EIO) {
+ }
+
+ kmem_cache_free(ubi_wl_entry_slab, e);
+ if (err != -EIO)
/*
* If this is not %-EIO, we have no idea what to do. Scheduling
* this physical eraseblock for erasure again would cause
* errors again and again. Well, lets switch to R/O mode.
*/
goto out_ro;
- }
/* It is %-EIO, the PEB went bad */
--
1.7.7.3
--
Best Regards,
Artem Bityutskiy
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^ permalink raw reply related [flat|nested] 3+ messages in thread