Re: [PATCH v3] gpio: cdev: fix kernel stack leak to user-space in error path

[Bartosz Golaszewski]

On Tue, 22 Sep 2026 11:09:55 +0200, Kent Gibson <warthog618@xxxxxxxxx> said:
> On Tue, Sep 22, 2026 at 10:52:28AM +0200, Bartosz Golaszewski wrote:
>> If we fail to acquire the GPIO chip guard in gpio_desc_to_lineinfo(), we
>> return immediately before zeroing the info struct we'll end up passing
>> to the user-space later in lineinfo_get_v1(). This may leak the kernel
>> stack contents. Make gpio_desc_to_lineinfo() return int so that the
>> -ENODEV returned on failure to acquire the guard can be propagated to
>> the callers.
>>
>> While not strictly necessary: move the memset() before trying to acquire
>> the SRCU read lock too for good measure.
>>
>> Fixes: d83cee3d2bb1 ("gpio: protect the pointer to gpio_chip in gpio_device with SRCU")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
>> Closes: https://sashiko.dev/#/patchset/20260912123529.7951-1-tzungbi%40kernel.org?part=3
>> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>
>> ---
>> Changes in v3:
>> - Don't emit an error log message from the line info notifier if we fail
>>   to acquire the chip guard
>> - Link to v2: https://patch.msgid.link/20260921-gpio-cdev-stack-leak-fixes-v2-1-3307c4320352@xxxxxxxxxxxxxxxx
>>
>> Changes in v2:
>> - Make gpio_desc_to_lineinfo() return an integer return value so that
>>   the error code returned in case of a failure to acquire the guard can
>>   be propagated down the stack
>> - Link to v1: https://patch.msgid.link/20260917-gpio-cdev-stack-leak-fixes-v1-1-2bb52879e49c@xxxxxxxxxxxxxxxx
>> ---
>>  drivers/gpio/gpiolib-cdev.c | 32 +++++++++++++++++++++++++-------
>>  1 file changed, 25 insertions(+), 7 deletions(-)
>>
>
>> @@ -2491,6 +2502,7 @@ static int lineinfo_changed_notify(struct notifier_block *nb,
>>  	struct lineinfo_changed_ctx *ctx;
>>  	struct gpio_desc *desc = data;
>>  	struct file *fp;
>> +	int ret;
>>
>>  	if (!test_bit(gpiod_hwgpio(desc), cdev->watched_lines))
>>  		return NOTIFY_DONE;
>> @@ -2521,7 +2533,13 @@ static int lineinfo_changed_notify(struct notifier_block *nb,
>>
>>  	ctx->chg.event_type = action;
>>  	ctx->chg.timestamp_ns = ktime_get_ns();
>> -	gpio_desc_to_lineinfo(desc, &ctx->chg.info, true);
>> +
>> +	ret = gpio_desc_to_lineinfo(desc, &ctx->chg.info, true);
>> +	if (ret) {
>> +		fput(fp);
>> +		return NOTIFY_DONE;
>> +	}
>> +
>
> Drop the ret and just test the return directly?
>
> Sorry - should've picked that up in the previous version.
>

I actually prefer the assignment, I find it more readable.

Bartosz