Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit f5c2742c authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

random: cap the rate which the /dev/urandom pool gets reseeded 



In order to avoid draining the input pool of its entropy at too high
of a rate, enforce a minimum time interval between reseedings of the
urandom pool.  This is set to 60 seconds by default.

Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent c59974ae

drivers/char/random.c

+24 −0
Original line number Diff line number Diff line
@@ -306,6 +306,13 @@ static int random_read_wakeup_thresh = 64; 
 */

static int random_write_wakeup_thresh = 128;



/*

 * The minimum number of seconds between urandom pool resending.  We

 * do this to limit the amount of entropy that can be drained from the

 * input pool even if there are heavy demands on /dev/urandom.

 */

static int random_min_urandom_seed = 60;



/*

 * When the input pool goes over trickle_thresh, start dropping most

 * samples to avoid wasting CPU time and reduce lock contention.
@@ -438,6 +445,7 @@ struct entropy_store { 
	struct entropy_store *pull;



	/* read-write data: */

	unsigned long last_pulled;

	spinlock_t lock;

	unsigned short add_ptr;

	unsigned short input_rotate;
@@ -887,6 +895,14 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes) 
{

	__u32	tmp[OUTPUT_POOL_WORDS];



	if (r->limit == 0 && random_min_urandom_seed) {

		unsigned long now = jiffies;



		if (time_before(now,

				r->last_pulled + random_min_urandom_seed * HZ))

			return;

		r->last_pulled = now;

	}

	if (r->pull &&

	    r->entropy_count < (nbytes << (ENTROPY_SHIFT + 3)) &&

	    r->entropy_count < r->poolinfo->poolfracbits) {
@@ -1190,6 +1206,7 @@ static void init_std_data(struct entropy_store *r) 
	r->entropy_count = 0;

	r->entropy_total = 0;

	r->last_data_init = 0;

	r->last_pulled = jiffies;

	mix_pool_bytes(r, &now, sizeof(now), NULL);

	for (i = r->poolinfo->poolbytes; i > 0; i -= sizeof(rv)) {

		if (!arch_get_random_long(&rv))
@@ -1540,6 +1557,13 @@ struct ctl_table random_table[] = { 
		.extra1		= &min_write_thresh,

		.extra2		= &max_write_thresh,

	},

	{

		.procname	= "urandom_min_reseed_secs",

		.data		= &random_min_urandom_seed,

		.maxlen		= sizeof(int),

		.mode		= 0644,

		.proc_handler	= proc_dointvec,

	},

	{

		.procname	= "boot_id",

		.data		= &sysctl_bootid,