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Commit 9372b35e authored by Rusty Russell's avatar Rusty Russell Committed by Herbert Xu
Browse files

hwrng: place mutex around read functions and buffers. 



There's currently a big lock around everything, and it means that we
can't query sysfs (eg /sys/devices/virtual/misc/hw_random/rng_current)
while the rng is reading.  This is a real problem when the rng is slow,
or blocked (eg. virtio_rng with qemu's default /dev/random backend)

This doesn't help (it leaves the current lock untouched), just adds a
lock to protect the read function and the static buffers, in preparation
for transition.

Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 25fb8638

drivers/char/hw_random/core.c

+17 −3
Original line number Diff line number Diff line
@@ -53,7 +53,10 @@ 
static struct hwrng *current_rng;

static struct task_struct *hwrng_fill;

static LIST_HEAD(rng_list);

/* Protects rng_list and current_rng */

static DEFINE_MUTEX(rng_mutex);

/* Protects rng read functions, data_avail, rng_buffer and rng_fillbuf */

static DEFINE_MUTEX(reading_mutex);

static int data_avail;

static u8 *rng_buffer, *rng_fillbuf;

static unsigned short current_quality;
@@ -81,7 +84,9 @@ static void add_early_randomness(struct hwrng *rng) 
	unsigned char bytes[16];

	int bytes_read;



	mutex_lock(&reading_mutex);

	bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);

	mutex_unlock(&reading_mutex);

	if (bytes_read > 0)

		add_device_randomness(bytes, bytes_read);

}
@@ -128,6 +133,7 @@ static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size, 
			int wait) {

	int present;



	BUG_ON(!mutex_is_locked(&reading_mutex));

	if (rng->read)

		return rng->read(rng, (void *)buffer, size, wait);
@@ -160,13 +166,14 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf, 
			goto out_unlock;

		}



		mutex_lock(&reading_mutex);

		if (!data_avail) {

			bytes_read = rng_get_data(current_rng, rng_buffer,

				rng_buffer_size(),

				!(filp->f_flags & O_NONBLOCK));

			if (bytes_read < 0) {

				err = bytes_read;

				goto out_unlock;

				goto out_unlock_reading;

			}

			data_avail = bytes_read;

		}
@@ -174,7 +181,7 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf, 
		if (!data_avail) {

			if (filp->f_flags & O_NONBLOCK) {

				err = -EAGAIN;

				goto out_unlock;

				goto out_unlock_reading;

			}

		} else {

			len = data_avail;
@@ -186,7 +193,7 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf, 
			if (copy_to_user(buf + ret, rng_buffer + data_avail,

								len)) {

				err = -EFAULT;

				goto out_unlock;

				goto out_unlock_reading;

			}



			size -= len;
@@ -194,6 +201,7 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf, 
		}



		mutex_unlock(&rng_mutex);

		mutex_unlock(&reading_mutex);



		if (need_resched())

			schedule_timeout_interruptible(1);
@@ -208,6 +216,9 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf, 
out_unlock:

	mutex_unlock(&rng_mutex);

	goto out;

out_unlock_reading:

	mutex_unlock(&reading_mutex);

	goto out_unlock;

}
@@ -344,13 +355,16 @@ static int hwrng_fillfn(void *unused) 
	while (!kthread_should_stop()) {

		if (!current_rng)

			break;

		mutex_lock(&reading_mutex);

		rc = rng_get_data(current_rng, rng_fillbuf,

				  rng_buffer_size(), 1);

		mutex_unlock(&reading_mutex);

		if (rc <= 0) {

			pr_warn("hwrng: no data available\n");

			msleep_interruptible(10000);

			continue;

		}

		/* Outside lock, sure, but y'know: randomness. */

		add_hwgenerator_randomness((void *)rng_fillbuf, rc,

					   rc * current_quality * 8 >> 10);

	}