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: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/drivers/char/random.c b/drivers/char/random.c
index a38d97a..0894d86 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -724,6 +724,8 @@
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 @@
}
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
@@ -1267,8 +1269,10 @@
* source.
*/
state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
- if (state)
+ if (state) {
+ state->last_time = INITIAL_JIFFIES;
disk->random = state;
+ }
}
#endif