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Commit 331c6490 authored by H. Peter Anvin's avatar H. Peter Anvin Committed by Theodore Ts'o
Browse files

random: If we have arch_get_random_seed*(), try it before blocking 



If we have arch_get_random_seed*(), try to use it for emergency refill
of the entropy pool before giving up and blocking on /dev/random.  It
may or may not work in the moment, but if it does work, it will give
the user better service than blocking will.

Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 83664a69

drivers/char/random.c

+33 −0
Original line number Original line Diff line number Diff line
@@ -1294,6 +1294,34 @@ void rand_initialize_disk(struct gendisk *disk) 
}

}

#endif

#endif





/*

 * Attempt an emergency refill using arch_get_random_seed_long().

 *

 * As with add_interrupt_randomness() be paranoid and only

 * credit the output as 50% entropic.

 */

static int arch_random_refill(void)

{

	const unsigned int nlongs = 64;	/* Arbitrary number */

	unsigned int n = 0;

	unsigned int i;

	unsigned long buf[nlongs];



	for (i = 0; i < nlongs; i++) {

		if (arch_get_random_seed_long(&buf[n]))

			n++;

	}



	if (n) {

		unsigned int rand_bytes = n * sizeof(unsigned long);



		mix_pool_bytes(&input_pool, buf, rand_bytes, NULL);

		credit_entropy_bits(&input_pool, rand_bytes*4);

	}



	return n;

}



static ssize_t

static ssize_t

random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)

random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)

{

{
@@ -1312,8 +1340,13 @@ random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) 
				  ENTROPY_BITS(&input_pool));

				  ENTROPY_BITS(&input_pool));

		if (n > 0)

		if (n > 0)

			return n;

			return n;



		/* Pool is (near) empty.  Maybe wait and retry. */

		/* Pool is (near) empty.  Maybe wait and retry. */





		/* First try an emergency refill */

		if (arch_random_refill())

			continue;



		if (file->f_flags & O_NONBLOCK)

		if (file->f_flags & O_NONBLOCK)

			return -EAGAIN;

			return -EAGAIN;