2023-10-12 23:10:29

by Ricardo B. Marliere

Subject: [PATCH] media: pvrusb2: fix use after free on context disconnection

Upon module load, a kthread is created targeting the
pvr2_context_thread_func function, which may call pvr2_context_destroy
and thus call kfree() on the context object. However, that might happen
before the usb hub_event handler is able to notify the driver. This
patch adds a sanity check before the invalid read reported by syzbot,
within the context disconnection call stack.

Fixes: e5be15c63804 ("V4L/DVB (7711): pvrusb2: Fix race on module unload")
Reported-and-tested-by: [email protected]
Closes: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Ricardo B. Marliere <[email protected]>
---
drivers/media/usb/pvrusb2/pvrusb2-context.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/pvrusb2/pvrusb2-context.c b/drivers/media/usb/pvrusb2/pvrusb2-context.c
index 14170a5d72b3..1764674de98b 100644
--- a/drivers/media/usb/pvrusb2/pvrusb2-context.c
+++ b/drivers/media/usb/pvrusb2/pvrusb2-context.c
@@ -268,7 +268,8 @@ void pvr2_context_disconnect(struct pvr2_context *mp)
{
pvr2_hdw_disconnect(mp->hdw);
mp->disconnect_flag = !0;
- pvr2_context_notify(mp);
+ if (!pvr2_context_shutok())
+ pvr2_context_notify(mp);
}


--
2.42.0

2023-10-16 01:55:22

by Mike Isely

Subject: Re: [PATCH] media: pvrusb2: fix use after free on context disconnection

Acked-by: Mike Isely <[email protected]>

-Mike

On Thu, 12 Oct 2023, Ricardo B. Marliere wrote:

> Upon module load, a kthread is created targeting the
> pvr2_context_thread_func function, which may call pvr2_context_destroy
> and thus call kfree() on the context object. However, that might happen
> before the usb hub_event handler is able to notify the driver. This
> patch adds a sanity check before the invalid read reported by syzbot,
> within the context disconnection call stack.
>
> Fixes: e5be15c63804 ("V4L/DVB (7711): pvrusb2: Fix race on module unload")
> Reported-and-tested-by: [email protected]
> Closes: https://lore.kernel.org/all/[email protected]/
> Signed-off-by: Ricardo B. Marliere <[email protected]>
> ---
> drivers/media/usb/pvrusb2/pvrusb2-context.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/usb/pvrusb2/pvrusb2-context.c b/drivers/media/usb/pvrusb2/pvrusb2-context.c
> index 14170a5d72b3..1764674de98b 100644
> --- a/drivers/media/usb/pvrusb2/pvrusb2-context.c
> +++ b/drivers/media/usb/pvrusb2/pvrusb2-context.c
> @@ -268,7 +268,8 @@ void pvr2_context_disconnect(struct pvr2_context *mp)
> {
> pvr2_hdw_disconnect(mp->hdw);
> mp->disconnect_flag = !0;
> - pvr2_context_notify(mp);
> + if (!pvr2_context_shutok())
> + pvr2_context_notify(mp);
> }
>
>
>