On Fri, 27 May 2016 09:45:49 -0700
Brian Norris <[email protected]> wrote:
> It seems like in the process of refactoring pwm_config() to utilize the
> newly-introduced pwm_apply_state() API, some args/bounds checking was
> dropped.
>
> In particular, I noted that we are now allowing invalid period
> selections. e.g.:
>
> # echo 1 > /sys/class/pwm/pwmchip0/export
> # cat /sys/class/pwm/pwmchip0/pwm1/period
> 100
> # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle
> [... driver may or may not reject the value, or trigger some logic bug ...]
>
> It's better to see:
>
> # echo 1 > /sys/class/pwm/pwmchip0/export
> # cat /sys/class/pwm/pwmchip0/pwm1/period
> 100
> # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle
> -bash: echo: write error: Invalid argument
>
> This patch reintroduces some bounds checks in both pwm_config() (for its
> signed parameters; we don't want to convert negative values into large
> unsigned values) and in pwm_apply_state() (which fix the above described
> behavior, as well as other potential API misuses).
>
> Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates")
> Signed-off-by: Brian Norris <[email protected]>
Acked-by: Boris Brezillon <[email protected]>
Thanks,
Boris
> ---
> v2:
> * changed subject, as this covers more scope now
> * add Fixes tag, as this is a v4.7-rc regression
> * add more bounds/args checks in pwm_apply_state() and pwm_config()
>
> drivers/pwm/core.c | 3 ++-
> include/linux/pwm.h | 3 +++
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index dba3843c53b8..ed337a8c34ab 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -457,7 +457,8 @@ int pwm_apply_state(struct pwm_device *pwm, struct
> pwm_state *state)
> {
> int err;
>
> - if (!pwm)
> + if (!pwm || !state || !state->period ||
> + state->duty_cycle > state->period)
> return -EINVAL;
>
> if (!memcmp(state, &pwm->state, sizeof(*state)))
> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> index 17018f3c066e..908b67c847cd 100644
> --- a/include/linux/pwm.h
> +++ b/include/linux/pwm.h
> @@ -235,6 +235,9 @@ static inline int pwm_config(struct pwm_device *pwm, int
> duty_ns,
> if (!pwm)
> return -EINVAL;
>
> + if (duty_ns < 0 || period_ns < 0)
> + return -EINVAL;
> +
> pwm_get_state(pwm, &state);
> if (state.duty_cycle == duty_ns && state.period == period_ns)
> return 0;
--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
