From f5245a5fdf757f50a6c905fc16cceb1a6146ccf5 Mon Sep 17 00:00:00 2001 From: David Lechner Date: Sun, 17 Oct 2021 13:55:21 -0500 Subject: [PATCH] counter: drop chrdev_lock This removes the chrdev_lock from the counter subsystem. This was intended to prevent opening the chrdev more than once. However, this doesn't work in practice since userspace can duplicate file descriptors and pass file descriptors to other processes. Since this protection can't be relied on, it is best to just remove it. Suggested-by: Greg KH Acked-by: William Breathitt Gray Signed-off-by: David Lechner Link: https://lore.kernel.org/r/20211017185521.3468640-1-david@lechnology.com Signed-off-by: Greg Kroah-Hartman --- drivers/counter/counter-chrdev.c | 6 ------ drivers/counter/counter-sysfs.c | 13 +++---------- include/linux/counter.h | 7 ------- 3 files changed, 3 insertions(+), 23 deletions(-) diff --git a/drivers/counter/counter-chrdev.c b/drivers/counter/counter-chrdev.c index 967c94a..b747dc8 100644 --- a/drivers/counter/counter-chrdev.c +++ b/drivers/counter/counter-chrdev.c @@ -384,10 +384,6 @@ static int counter_chrdev_open(struct inode *inode, struct file *filp) typeof(*counter), chrdev); - /* Ensure chrdev is not opened more than 1 at a time */ - if (!atomic_add_unless(&counter->chrdev_lock, 1, 1)) - return -EBUSY; - get_device(&counter->dev); filp->private_data = counter; @@ -419,7 +415,6 @@ out_unlock: mutex_unlock(&counter->ops_exist_lock); put_device(&counter->dev); - atomic_dec(&counter->chrdev_lock); return ret; } @@ -445,7 +440,6 @@ int counter_chrdev_add(struct counter_device *const counter) mutex_init(&counter->events_lock); /* Initialize character device */ - atomic_set(&counter->chrdev_lock, 0); cdev_init(&counter->chrdev, &counter_fops); /* Allocate Counter events queue */ diff --git a/drivers/counter/counter-sysfs.c b/drivers/counter/counter-sysfs.c index c2fddbb..8c2d7c2 100644 --- a/drivers/counter/counter-sysfs.c +++ b/drivers/counter/counter-sysfs.c @@ -796,25 +796,18 @@ static int counter_events_queue_size_write(struct counter_device *counter, u64 val) { DECLARE_KFIFO_PTR(events, struct counter_event); - int err = 0; - - /* Ensure chrdev is not opened more than 1 at a time */ - if (!atomic_add_unless(&counter->chrdev_lock, 1, 1)) - return -EBUSY; + int err; /* Allocate new events queue */ err = kfifo_alloc(&events, val, GFP_KERNEL); if (err) - goto exit_early; + return err; /* Swap in new events queue */ kfifo_free(&counter->events); counter->events.kfifo = events.kfifo; -exit_early: - atomic_dec(&counter->chrdev_lock); - - return err; + return 0; } static struct counter_comp counter_num_signals_comp = diff --git a/include/linux/counter.h b/include/linux/counter.h index 22b14a5..0fd99e2 100644 --- a/include/linux/counter.h +++ b/include/linux/counter.h @@ -297,7 +297,6 @@ struct counter_ops { * @events: queue of detected Counter events * @events_wait: wait queue to allow blocking reads of Counter events * @events_lock: lock to protect Counter events queue read operations - * @chrdev_lock: lock to limit chrdev to a single open at a time * @ops_exist_lock: lock to prevent use during removal */ struct counter_device { @@ -325,12 +324,6 @@ struct counter_device { DECLARE_KFIFO_PTR(events, struct counter_event); wait_queue_head_t events_wait; struct mutex events_lock; - /* - * chrdev_lock is locked by counter_chrdev_open() and unlocked by - * counter_chrdev_release(), so a mutex is not possible here because - * chrdev_lock will invariably be held when returning to user space - */ - atomic_t chrdev_lock; struct mutex ops_exist_lock; }; -- 2.7.4