2019-08-29 12:31:00

by Dan Carpenter

Subject: [PATCH] staging: greybus: light: fix a couple double frees

The problem is in gb_lights_request_handler(). If we get a request to
change the config then we release the light with gb_lights_light_release()
and re-allocated it. However, if the allocation fails part way through
then we call gb_lights_light_release() again. This can lead to a couple
different double frees where we haven't cleared out the original values:

gb_lights_light_v4l2_unregister(light);
...
kfree(light->channels);
kfree(light->name);

I also made a small change to how we set "light->channels_count = 0;".
The original code handled this part fine and did not cause a use after
free but it was sort of complicated to read.

Fixes: 2870b52bae4c ("greybus: lights: add lights implementation")
Signed-off-by: Dan Carpenter <[email protected]>
---
drivers/staging/greybus/light.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/greybus/light.c b/drivers/staging/greybus/light.c
index 010ae1e9c7fb..40680eaf3974 100644
--- a/drivers/staging/greybus/light.c
+++ b/drivers/staging/greybus/light.c
@@ -1098,21 +1098,21 @@ static void gb_lights_channel_release(struct gb_channel *channel)
static void gb_lights_light_release(struct gb_light *light)
{
int i;
- int count;

light->ready = false;

- count = light->channels_count;
-
if (light->has_flash)
gb_lights_light_v4l2_unregister(light);
+ light->has_flash = false;

- for (i = 0; i < count; i++) {
+ for (i = 0; i < light->channels_count; i++)
gb_lights_channel_release(&light->channels[i]);
- light->channels_count--;
- }
+ light->channels_count = 0;
+
kfree(light->channels);
+ light->channels = NULL;
kfree(light->name);
+ light->name = NULL;
}

static void gb_lights_release(struct gb_lights *glights)
--
2.20.1

2019-08-29 14:56:30

by Rui Miguel Silva

Subject: Re: [PATCH] staging: greybus: light: fix a couple double frees

Hi Dan,
On Thu 29 Aug 2019 at 13:28, Dan Carpenter wrote:
> The problem is in gb_lights_request_handler(). If we get a request to
> change the config then we release the light with gb_lights_light_release()
> and re-allocated it. However, if the allocation fails part way through
> then we call gb_lights_light_release() again. This can lead to a couple
> different double frees where we haven't cleared out the original values:
>
> gb_lights_light_v4l2_unregister(light);
> ...
> kfree(light->channels);
> kfree(light->name);
>
> I also made a small change to how we set "light->channels_count = 0;".
> The original code handled this part fine and did not cause a use after
> free but it was sort of complicated to read.
>
> Fixes: 2870b52bae4c ("greybus: lights: add lights implementation")
> Signed-off-by: Dan Carpenter <[email protected]>
>

Thanks so much for this, I was looking for some time at this and
was half way to a much less elegant fix then yours.

Acked-by: Rui Miguel Silva <[email protected]>

Cheers,
Rui

> ---
> drivers/staging/greybus/light.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/staging/greybus/light.c b/drivers/staging/greybus/light.c
> index 010ae1e9c7fb..40680eaf3974 100644
> --- a/drivers/staging/greybus/light.c
> +++ b/drivers/staging/greybus/light.c
> @@ -1098,21 +1098,21 @@ static void gb_lights_channel_release(struct gb_channel *channel)
> static void gb_lights_light_release(struct gb_light *light)
> {
> int i;
> - int count;
>
> light->ready = false;
>
> - count = light->channels_count;
> -
> if (light->has_flash)
> gb_lights_light_v4l2_unregister(light);
> + light->has_flash = false;
>
> - for (i = 0; i < count; i++) {
> + for (i = 0; i < light->channels_count; i++)
> gb_lights_channel_release(&light->channels[i]);
> - light->channels_count--;
> - }
> + light->channels_count = 0;
> +
> kfree(light->channels);
> + light->channels = NULL;
> kfree(light->name);
> + light->name = NULL;
> }
>
> static void gb_lights_release(struct gb_lights *glights)