Re: [PATCH v2] acer-wmi: fix memory leaks in wmab_execute error path

[Axel Lin]

2010/7/13 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>:
> On Fri, 09 Jul 2010 12:37:36 +0800 Axel Lin <axel.lin@xxxxxxxxx> wrote:
>
>> When acpi_evaluate_object() is passed ACPI_ALLOCATE_BUFFER,
>> the caller must kfree the returned buffer if AE_OK is returned.
>>
>> Call Trace:
>> wmab_execute
>>   -> wmi_evaluate_method
>>     -> acpi_evaluate_object
>>
>> Thus if callers of wmab_execute() pass ACPI_ALLOCATE_BUFFER,
>> the return buffer must be kfreed if wmab_execute return AE_OK.
>>
>> Signed-off-by: Axel Lin <axel.lin@xxxxxxxxx>
>> ---
>>  drivers/platform/x86/acer-wmi.c |   11 ++++++++++-
>>  1 files changed, 10 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/platform/x86/acer-wmi.c b/drivers/platform/x86/acer-wmi.c
>> index 1ea6c43..3f44446 100644
>> --- a/drivers/platform/x86/acer-wmi.c
>> +++ b/drivers/platform/x86/acer-wmi.c
>> @@ -555,6 +555,7 @@ static acpi_status AMW0_find_mailled(void)
>>       obj->buffer.length == sizeof(struct wmab_ret)) {
>>               ret = *((struct wmab_ret *) obj->buffer.pointer);
>>       } else {
>> +             kfree(out.pointer);
>>               return AE_ERROR;
>>       }
>>
>> @@ -598,6 +599,7 @@ static acpi_status AMW0_set_capabilities(void)
>>       obj->buffer.length == sizeof(struct wmab_ret)) {
>>               ret = *((struct wmab_ret *) obj->buffer.pointer);
>>       } else {
>> +             kfree(out.pointer);
>>               return AE_ERROR;
>>       }
>>
>> @@ -607,15 +609,22 @@ static acpi_status AMW0_set_capabilities(void)
>>       args.ebx = 2 << 8;
>>       args.ebx |= ACER_AMW0_BLUETOOTH_MASK;
>>
>> +     /*
>> +      * It's ok to use existing buffer for next wmab_execute call.
>> +      * But we need to kfree(out.pointer) if next wmab_execute fail.
>> +      */
>>       status = wmab_execute(&args, &out);
>> -     if (ACPI_FAILURE(status))
>> +     if (ACPI_FAILURE(status)) {
>> +             kfree(out.pointer);
>>               return status;
>> +     }
>>
>>       obj = (union acpi_object *) out.pointer;
>>       if (obj && obj->type == ACPI_TYPE_BUFFER
>>       && obj->buffer.length == sizeof(struct wmab_ret)) {
>>               ret = *((struct wmab_ret *) obj->buffer.pointer);
>>       } else {
>> +             kfree(out.pointer);
>>               return AE_ERROR;
>>       }
>
> I think it's best to remove the multiple-return-points approach in
> favour of the "goto single return point which undoes things" approach.
> that way we reduce the risk of later introducing more leaks.
>
> Please review:
>
> From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>
> avoid multiple return points
> remove unneeded cast
> remove unneeded initialisation of `status'
>
> Cc: Alan Jenkins <alan-jenkins@xxxxxxxxxxxxxx>
> Cc: Axel Lin <axel.lin@xxxxxxxxx>
> Cc: Carlos Corbacho <carlos@xxxxxxxxxxxxxxxxxxx>
> Cc: Matthew Garrett <mjg@xxxxxxxxxx>
> Cc: Thomas Renninger <trenn@xxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

I'm not the author, but since I'm in the CC list and it looks good to me.
Acked-by: Axel Lin <axel.lin@xxxxxxxxx>

> ---
>
>  drivers/platform/x86/acer-wmi.c |   25 ++++++++++++-------------
>  1 file changed, 12 insertions(+), 13 deletions(-)
>
> diff -puN drivers/platform/x86/acer-wmi.c~acer-wmi-fix-memory-leaks-in-wmab_execute-error-path-v2-fix drivers/platform/x86/acer-wmi.c
> --- a/drivers/platform/x86/acer-wmi.c~acer-wmi-fix-memory-leaks-in-wmab_execute-error-path-v2-fix
> +++ a/drivers/platform/x86/acer-wmi.c
> @@ -571,7 +571,7 @@ static acpi_status AMW0_set_capabilities
>  {
>        struct wmab_args args;
>        struct wmab_ret ret;
> -       acpi_status status = AE_OK;
> +       acpi_status status;
>        struct acpi_buffer out = { ACPI_ALLOCATE_BUFFER, NULL };
>        union acpi_object *obj;
>
> @@ -594,13 +594,13 @@ static acpi_status AMW0_set_capabilities
>        if (ACPI_FAILURE(status))
>                return status;
>
> -       obj = (union acpi_object *) out.pointer;
> +       obj = out.pointer;
>        if (obj && obj->type == ACPI_TYPE_BUFFER &&
>        obj->buffer.length == sizeof(struct wmab_ret)) {
>                ret = *((struct wmab_ret *) obj->buffer.pointer);
>        } else {
> -               kfree(out.pointer);
> -               return AE_ERROR;
> +               status = AE_ERROR;
> +               goto out;
>        }
>
>        if (ret.eax & 0x1)
> @@ -614,25 +614,21 @@ static acpi_status AMW0_set_capabilities
>         * But we need to kfree(out.pointer) if next wmab_execute fail.
>         */
>        status = wmab_execute(&args, &out);
> -       if (ACPI_FAILURE(status)) {
> -               kfree(out.pointer);
> -               return status;
> -       }
> +       if (ACPI_FAILURE(status))
> +               goto out;
>
>        obj = (union acpi_object *) out.pointer;
>        if (obj && obj->type == ACPI_TYPE_BUFFER
>        && obj->buffer.length == sizeof(struct wmab_ret)) {
>                ret = *((struct wmab_ret *) obj->buffer.pointer);
>        } else {
> -               kfree(out.pointer);
> -               return AE_ERROR;
> +               status = AE_ERROR;
> +               goto out;
>        }
>
>        if (ret.eax & 0x1)
>                interface->capability |= ACER_CAP_BLUETOOTH;
>
> -       kfree(out.pointer);
> -
>        /*
>         * This appears to be safe to enable, since all Wistron based laptops
>         * appear to use the same EC register for brightness, even if they
> @@ -641,7 +637,10 @@ static acpi_status AMW0_set_capabilities
>        if (quirks->brightness >= 0)
>                interface->capability |= ACER_CAP_BRIGHTNESS;
>
> -       return AE_OK;
> +       status = AE_OK;
> +out:
> +       kfree(out.pointer);
> +       return status;
>  }
>
>  static struct wmi_interface AMW0_interface = {
> _
>
>
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