[PATCH v2 0/2] Fix two kernel warnings in glink driver

[PATCH v2 0/2] Fix two kernel warnings in glink driver

[Sujit Kautkar]

    These changes addresses kernel warnings which shows up after enabling
    debug kernel. First one fixes use-after-free warning and second fixes
    warning by updating cdev APIs

    Changes in v2:
    - Fix typo in commit message

Sujit Kautkar (2):
  rpmsg: glink: Fix use-after-free in qcom_glink_rpdev_release()
  rpmsg: glink: Update cdev add/del API in
    rpmsg_ctrldev_release_device()

 drivers/rpmsg/qcom_glink_native.c | 5 ++++-
 drivers/rpmsg/rpmsg_char.c        | 5 ++---
 2 files changed, 6 insertions(+), 4 deletions(-)

-- 
2.31.0

[PATCH v2 1/2] rpmsg: glink: Fix use-after-free in qcom_glink_rpdev_release()

[Sujit Kautkar]

qcom_glink_rpdev_release() sets channel->rpdev to NULL. However, with
debug enabled kernel, qcom_glink_rpdev_release() gets delayed due to
delayed kobject release and channel gets released by that time and
triggers below kernel warning. To avoid this use-after-free, add a
condition to checks if channel was already released.

| BUG: KASAN: use-after-free in qcom_glink_rpdev_release+0x54/0x70
| Write of size 8 at addr ffffffaba438e8d0 by task kworker/6:1/54
|
| CPU: 6 PID: 54 Comm: kworker/6:1 Not tainted 5.4.109-lockdep #16
| Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
| Workqueue: events kobject_delayed_cleanup
| Call trace:
|  dump_backtrace+0x0/0x284
|  show_stack+0x20/0x2c
|  dump_stack+0xd4/0x170
|  print_address_description+0x3c/0x4a8
|  __kasan_report+0x144/0x168
|  kasan_report+0x10/0x18
|  __asan_report_store8_noabort+0x1c/0x24
|  qcom_glink_rpdev_release+0x54/0x70
|  device_release+0x68/0x14c
|  kobject_delayed_cleanup+0x158/0x2cc
|  process_one_work+0x7cc/0x10a4
|  worker_thread+0x80c/0xcec
|  kthread+0x2a8/0x314
|  ret_from_fork+0x10/0x18

Signed-off-by: Sujit Kautkar <sujitka@chromium.org>
---

(no changes since v1)

 drivers/rpmsg/qcom_glink_native.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/rpmsg/qcom_glink_native.c b/drivers/rpmsg/qcom_glink_native.c
index e1444fefdd1c0..cc3556a9385a9 100644
--- a/drivers/rpmsg/qcom_glink_native.c
+++ b/drivers/rpmsg/qcom_glink_native.c
@@ -270,6 +270,7 @@ static void qcom_glink_channel_release(struct kref *ref)
 	spin_unlock_irqrestore(&channel->intent_lock, flags);
 
 	kfree(channel->name);
+	channel = NULL;
 	kfree(channel);
 }
 
@@ -1372,8 +1373,10 @@ static void qcom_glink_rpdev_release(struct device *dev)
 {
 	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
 	struct glink_channel *channel = to_glink_channel(rpdev->ept);
+	if (channel) {
+		channel->rpdev = NULL;
+	}
 
-	channel->rpdev = NULL;
 	kfree(rpdev);
 }
 
-- 
2.31.0

Re: [PATCH v2 1/2] rpmsg: glink: Fix use-after-free in qcom_glink_rpdev_release()

[Matthias Kaehlcke]

On Mon, Oct 25, 2021 at 04:37:52PM -0700, Sujit Kautkar wrote:
> qcom_glink_rpdev_release() sets channel->rpdev to NULL. However, with
> debug enabled kernel, qcom_glink_rpdev_release() gets delayed due to
> delayed kobject release and channel gets released by that time and
> triggers below kernel warning. To avoid this use-after-free, add a
> condition to checks if channel was already released.
> 
> | BUG: KASAN: use-after-free in qcom_glink_rpdev_release+0x54/0x70
> | Write of size 8 at addr ffffffaba438e8d0 by task kworker/6:1/54
> |
> | CPU: 6 PID: 54 Comm: kworker/6:1 Not tainted 5.4.109-lockdep #16
> | Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
> | Workqueue: events kobject_delayed_cleanup
> | Call trace:
> |  dump_backtrace+0x0/0x284
> |  show_stack+0x20/0x2c
> |  dump_stack+0xd4/0x170
> |  print_address_description+0x3c/0x4a8
> |  __kasan_report+0x144/0x168
> |  kasan_report+0x10/0x18
> |  __asan_report_store8_noabort+0x1c/0x24
> |  qcom_glink_rpdev_release+0x54/0x70
> |  device_release+0x68/0x14c
> |  kobject_delayed_cleanup+0x158/0x2cc
> |  process_one_work+0x7cc/0x10a4
> |  worker_thread+0x80c/0xcec
> |  kthread+0x2a8/0x314
> |  ret_from_fork+0x10/0x18
> 
> Signed-off-by: Sujit Kautkar <sujitka@chromium.org>
> ---
> 
> (no changes since v1)
> 
>  drivers/rpmsg/qcom_glink_native.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rpmsg/qcom_glink_native.c b/drivers/rpmsg/qcom_glink_native.c
> index e1444fefdd1c0..cc3556a9385a9 100644
> --- a/drivers/rpmsg/qcom_glink_native.c
> +++ b/drivers/rpmsg/qcom_glink_native.c
> @@ -270,6 +270,7 @@ static void qcom_glink_channel_release(struct kref *ref)
>  	spin_unlock_irqrestore(&channel->intent_lock, flags);
>  
>  	kfree(channel->name);
> +	channel = NULL;

This doesn't make much sense, 'channel' is a local variable, the only effect
this has is that the memory of 'channel' isn't freed by the 'kfree' below.

Maybe this is debug code and wasn't intended to be part of this patch?

>  	kfree(channel);
>  }
>  
> @@ -1372,8 +1373,10 @@ static void qcom_glink_rpdev_release(struct device *dev)
>  {
>  	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
>  	struct glink_channel *channel = to_glink_channel(rpdev->ept);
> +	if (channel) {
> +		channel->rpdev = NULL;
> +	}

Remove curly braces for single line branch.

>  
> -	channel->rpdev = NULL;
>  	kfree(rpdev);
>  }
>  
> -- 
> 2.31.0
>