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Commit 644008df authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

random: initialize the last_time field in struct timer_rand_state 



Since we initialize jiffies to wrap five minutes before boot (see
INITIAL_JIFFIES defined in include/linux/jiffies.h) it's important to
make sure the last_time field is initialized to INITIAL_JIFFIES.
Otherwise, the entropy estimator will overestimate the amount of
entropy resulting from the first call to add_timer_randomness(),
generally by about 8 bits.

Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent ae9ecd92

drivers/char/random.c

+6 −2
Original line number Diff line number Diff line
@@ -724,6 +724,8 @@ struct timer_rand_state { 
	unsigned dont_count_entropy:1;

};



#define INIT_TIMER_RAND_STATE { INITIAL_JIFFIES, };



/*

 * Add device- or boot-specific data to the input and nonblocking

 * pools to help initialize them to unique values.
@@ -750,7 +752,7 @@ void add_device_randomness(const void *buf, unsigned int size) 
}

EXPORT_SYMBOL(add_device_randomness);



static struct timer_rand_state input_timer_state;

static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_STATE;



/*

 * This function adds entropy to the entropy "pool" by using timing
@@ -1267,9 +1269,11 @@ void rand_initialize_disk(struct gendisk *disk) 
	 * source.

	 */

	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);

	if (state)

	if (state) {

		state->last_time = INITIAL_JIFFIES;

		disk->random = state;

	}

}

#endif



static ssize_t