From 33b96d934902f96e901b72ac18bbc47afad1ac20 Mon Sep 17 00:00:00 2001 From: Elias Vanderstuyft Date: Wed, 14 Oct 2015 17:29:37 -0700 Subject: [PATCH] Input: document and check on implicitly defined FF_MAX_EFFECTS 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 Signed-off-by: Dmitry Torokhov --- 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 eab56c0..8f20424 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 a8e74b4..4f9f2a0 100644 --- a/include/uapi/linux/input.h +++ b/include/uapi/linux/input.h @@ -414,6 +414,14 @@ 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) -- 2.7.4