[PATCH] rpmsg: char: Avoid double destroy of default endpoint

[PATCH] rpmsg: char: Avoid double destroy of default endpoint

[Shengjiu Wang]

The rpmsg_dev_remove() in rpmsg_core is the place for releasing
this default endpoint.

So need to avoid destroying the default endpoint in
rpmsg_chrdev_eptdev_destroy(), this should be the same as
rpmsg_eptdev_release(). Otherwise there will be double destroy
issue that ept->refcount report warning:

refcount_t: underflow; use-after-free.

Call trace:
 refcount_warn_saturate+0xf8/0x150
 virtio_rpmsg_destroy_ept+0xd4/0xec
 rpmsg_dev_remove+0x60/0x70

Fixes: bea9b79c2d10 ("rpmsg: char: Add possibility to use default endpoint of the rpmsg device")
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
---
 drivers/rpmsg/rpmsg_char.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index 0850ae34fb88..562d545ac0d3 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -76,7 +76,8 @@ int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
 
 	mutex_lock(&eptdev->ept_lock);
 	if (eptdev->ept) {
-		rpmsg_destroy_ept(eptdev->ept);
+		if (!eptdev->default_ept)
+			rpmsg_destroy_ept(eptdev->ept);
 		eptdev->ept = NULL;
 	}
 	mutex_unlock(&eptdev->ept_lock);
-- 
2.34.1

Re: [PATCH] rpmsg: char: Avoid double destroy of default endpoint

[Mathieu Poirier]

On Fri, 16 Sept 2022 at 00:57, Shengjiu Wang <shengjiu.wang@nxp.com> wrote:
>
> The rpmsg_dev_remove() in rpmsg_core is the place for releasing
> this default endpoint.
>
> So need to avoid destroying the default endpoint in
> rpmsg_chrdev_eptdev_destroy(), this should be the same as
> rpmsg_eptdev_release(). Otherwise there will be double destroy
> issue that ept->refcount report warning:
>
> refcount_t: underflow; use-after-free.
>
> Call trace:
>  refcount_warn_saturate+0xf8/0x150
>  virtio_rpmsg_destroy_ept+0xd4/0xec
>  rpmsg_dev_remove+0x60/0x70
>
> Fixes: bea9b79c2d10 ("rpmsg: char: Add possibility to use default endpoint of the rpmsg device")
> Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
> ---
>  drivers/rpmsg/rpmsg_char.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> index 0850ae34fb88..562d545ac0d3 100644
> --- a/drivers/rpmsg/rpmsg_char.c
> +++ b/drivers/rpmsg/rpmsg_char.c
> @@ -76,7 +76,8 @@ int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
>
>         mutex_lock(&eptdev->ept_lock);
>         if (eptdev->ept) {
> -               rpmsg_destroy_ept(eptdev->ept);
> +               if (!eptdev->default_ept)
> +                       rpmsg_destroy_ept(eptdev->ept);
>                 eptdev->ept = NULL;

Arnaud - please look into this one.

Thanks,
Mathieu

>         }
>         mutex_unlock(&eptdev->ept_lock);
> --
> 2.34.1
>

Re: [PATCH] rpmsg: char: Avoid double destroy of default endpoint

[Arnaud POULIQUEN]

Hello Shengjiu,

On 9/16/22 08:39, Shengjiu Wang wrote:
> The rpmsg_dev_remove() in rpmsg_core is the place for releasing
> this default endpoint.
> 
> So need to avoid destroying the default endpoint in
> rpmsg_chrdev_eptdev_destroy(), this should be the same as
> rpmsg_eptdev_release(). Otherwise there will be double destroy
> issue that ept->refcount report warning:
> 
> refcount_t: underflow; use-after-free.
> 
> Call trace:
>  refcount_warn_saturate+0xf8/0x150
>  virtio_rpmsg_destroy_ept+0xd4/0xec
>  rpmsg_dev_remove+0x60/0x70
> 
> Fixes: bea9b79c2d10 ("rpmsg: char: Add possibility to use default endpoint of the rpmsg device")
> Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
> ---
>  drivers/rpmsg/rpmsg_char.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> index 0850ae34fb88..562d545ac0d3 100644
> --- a/drivers/rpmsg/rpmsg_char.c
> +++ b/drivers/rpmsg/rpmsg_char.c
> @@ -76,7 +76,8 @@ int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
>  
>  	mutex_lock(&eptdev->ept_lock);
>  	if (eptdev->ept) {
> -		rpmsg_destroy_ept(eptdev->ept);
> +		if (!eptdev->default_ept)
> +			rpmsg_destroy_ept(eptdev->ept);
>  		eptdev->ept = NULL;
>  	}
>  	mutex_unlock(&eptdev->ept_lock);


Good catch!
I tried to reproduce it but without success. Do you set a specific config?

Concerning the patch:

Could you add a comment, to help to understand the condition?
something like "The default endpoint is released by the rpmsg core"

With that Reviewed-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>

Thanks,
Arnaud