2023-07-31 13:46:33

by Usyskin, Alexander

Subject: [PATCH v2] mtd: fix use-after-free in mtd release

I case of partition device_unregister() in mtd_device_release()
calls mtd_release() which frees mtd_info structure for partition.
All code after device_unregister in mtd_device_release thus
uses already freed memory.

Move part of code to mtd_release() and restict mtd->dev cleanup
to non-partion object.
For partition object such cleanup have no sense as partition
mtd_info is removed.

Cc: Miquel Raynal <[email protected]>
Cc: Zhang Xiaoxu <[email protected]>
Fixes: 19bfa9ebebb5 ("mtd: use refcount to prevent corruption")
Reviewed-by: Tomas Winkler <[email protected]>
Signed-off-by: Alexander Usyskin <[email protected]>
---

V2: Fix commit messsge wording

---
drivers/mtd/mtdcore.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 2466ea466466..46f15f676491 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -93,6 +93,9 @@ static void mtd_release(struct device *dev)
struct mtd_info *mtd = dev_get_drvdata(dev);
dev_t index = MTD_DEVT(mtd->index);

+ idr_remove(&mtd_idr, mtd->index);
+ of_node_put(mtd_get_of_node(mtd));
+
if (mtd_is_partition(mtd))
release_mtd_partition(mtd);

@@ -103,6 +106,7 @@ static void mtd_release(struct device *dev)
static void mtd_device_release(struct kref *kref)
{
struct mtd_info *mtd = container_of(kref, struct mtd_info, refcnt);
+ bool is_partition = mtd_is_partition(mtd);

debugfs_remove_recursive(mtd->dbg.dfs_dir);

@@ -111,11 +115,13 @@ static void mtd_device_release(struct kref *kref)

device_unregister(&mtd->dev);

- /* Clear dev so mtd can be safely re-registered later if desired */
- memset(&mtd->dev, 0, sizeof(mtd->dev));
-
- idr_remove(&mtd_idr, mtd->index);
- of_node_put(mtd_get_of_node(mtd));
+ /*
+ * Clear dev so mtd can be safely re-registered later if desired.
+ * Should not be done for partition,
+ * as it was already destroyed in device_unregister().
+ */
+ if (!is_partition)
+ memset(&mtd->dev, 0, sizeof(mtd->dev));

module_put(THIS_MODULE);
}
--
2.34.1

2023-08-04 07:30:23

by Miquel Raynal

Subject: Re: [PATCH v2] mtd: fix use-after-free in mtd release

On Mon, 2023-07-31 at 11:58:36 UTC, Alexander Usyskin wrote:
> I case of partition device_unregister() in mtd_device_release()
> calls mtd_release() which frees mtd_info structure for partition.
> All code after device_unregister in mtd_device_release thus
> uses already freed memory.
>
> Move part of code to mtd_release() and restict mtd->dev cleanup
> to non-partion object.
> For partition object such cleanup have no sense as partition
> mtd_info is removed.
>
> Cc: Miquel Raynal <[email protected]>
> Cc: Zhang Xiaoxu <[email protected]>
> Fixes: 19bfa9ebebb5 ("mtd: use refcount to prevent corruption")
> Reviewed-by: Tomas Winkler <[email protected]>
> Signed-off-by: Alexander Usyskin <[email protected]>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/next, thanks.

Miquel