| Message ID | 1442510988-3164-2-git-send-email-elias.vds@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
On Thu, Sep 17, 2015 at 07:29:47PM +0200, Elias Vanderstuyft wrote: > There is an undocumented upper bound for the total number of ff effects: > FF_GAIN (= 96). > This can be found as follows: > - user: write(EV_FF, effect_id, iterations) > calls kernel: ff->playback(effect_id, ...): starts effect "effect_id" > - user: write(EV_FF, FF_GAIN, gain) > calls kernel: ff->set_gain(gain, ...): sets gain > > A collision occurs when effect_id equals FF_GAIN. > According to input_ff_event(), > FF_GAIN is the smallest value where a collision occurs. > Therefore the greatest safe value for effect_id is FF_GAIN - 1, > and thus the total number of effects should never exceed FF_GAIN. > > Define FF_MAX_EFFECTS as FF_GAIN and check on this limit in ff-core. > > Signed-off-by: Elias Vanderstuyft <elias.vds@gmail.com> Applied, thank you. > --- > drivers/input/ff-core.c | 5 +++++ > include/uapi/linux/input.h | 8 ++++++++ > 2 files changed, 13 insertions(+) > > diff --git a/drivers/input/ff-core.c b/drivers/input/ff-core.c > index c642082..0bf7008 100644 > --- a/drivers/input/ff-core.c > +++ b/drivers/input/ff-core.c > @@ -318,6 +318,11 @@ int input_ff_create(struct input_dev *dev, unsigned int max_effects) > return -EINVAL; > } > > + if (max_effects > FF_MAX_EFFECTS) { > + dev_err(&dev->dev, "cannot allocate more than FF_MAX_EFFECTS effects\n"); > + return -EINVAL; > + } > + > ff_dev_size = sizeof(struct ff_device) + > max_effects * sizeof(struct file *); > if (ff_dev_size < max_effects) /* overflow */ > diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h > index 63915a7..42d7933 100644 > --- a/include/uapi/linux/input.h > +++ b/include/uapi/linux/input.h > @@ -1200,6 +1200,14 @@ struct ff_effect { > #define FF_GAIN 0x60 > #define FF_AUTOCENTER 0x61 > > +/* > + * ff->playback(effect_id = FF_GAIN) is the first effect_id to > + * cause a collision with another ff method, in this case ff->set_gain(). > + * Therefore the greatest safe value for effect_id is FF_GAIN - 1, > + * and thus the total number of effects should never exceed FF_GAIN. > + */ > +#define FF_MAX_EFFECTS FF_GAIN > + > #define FF_MAX 0x7f > #define FF_CNT (FF_MAX+1) > > -- > 1.9.3 >
diff --git a/drivers/input/ff-core.c b/drivers/input/ff-core.c index c642082..0bf7008 100644 --- a/drivers/input/ff-core.c +++ b/drivers/input/ff-core.c @@ -318,6 +318,11 @@ int input_ff_create(struct input_dev *dev, unsigned int max_effects) return -EINVAL; } + if (max_effects > FF_MAX_EFFECTS) { + dev_err(&dev->dev, "cannot allocate more than FF_MAX_EFFECTS effects\n"); + return -EINVAL; + } + ff_dev_size = sizeof(struct ff_device) + max_effects * sizeof(struct file *); if (ff_dev_size < max_effects) /* overflow */ diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h index 63915a7..42d7933 100644 --- a/include/uapi/linux/input.h +++ b/include/uapi/linux/input.h @@ -1200,6 +1200,14 @@ struct ff_effect { #define FF_GAIN 0x60 #define FF_AUTOCENTER 0x61 +/* + * ff->playback(effect_id = FF_GAIN) is the first effect_id to + * cause a collision with another ff method, in this case ff->set_gain(). + * Therefore the greatest safe value for effect_id is FF_GAIN - 1, + * and thus the total number of effects should never exceed FF_GAIN. + */ +#define FF_MAX_EFFECTS FF_GAIN + #define FF_MAX 0x7f #define FF_CNT (FF_MAX+1)
There is an undocumented upper bound for the total number of ff effects: FF_GAIN (= 96). This can be found as follows: - user: write(EV_FF, effect_id, iterations) calls kernel: ff->playback(effect_id, ...): starts effect "effect_id" - user: write(EV_FF, FF_GAIN, gain) calls kernel: ff->set_gain(gain, ...): sets gain A collision occurs when effect_id equals FF_GAIN. According to input_ff_event(), FF_GAIN is the smallest value where a collision occurs. Therefore the greatest safe value for effect_id is FF_GAIN - 1, and thus the total number of effects should never exceed FF_GAIN. Define FF_MAX_EFFECTS as FF_GAIN and check on this limit in ff-core. Signed-off-by: Elias Vanderstuyft <elias.vds@gmail.com> --- drivers/input/ff-core.c | 5 +++++ include/uapi/linux/input.h | 8 ++++++++ 2 files changed, 13 insertions(+)