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| author | Theodore Ts'o <tytso@mit.edu> | 2013-09-22 15:14:32 -0400 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2013-10-10 14:32:19 -0400 |
| commit | f5c2742c23886e707f062881c5f206c1fc704782 (patch) | |
| tree | 3acaa54c3f8e4dd55723b1c93ae36cbc648ad2bf | |
| parent | c59974aea43fd292a0784dbf7b3d7347e2caf4e9 (diff) | |
| download | op-kernel-dev-f5c2742c23886e707f062881c5f206c1fc704782.zip op-kernel-dev-f5c2742c23886e707f062881c5f206c1fc704782.tar.gz | |
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: "Theodore Ts'o" <tytso@mit.edu>
| -rw-r--r-- | drivers/char/random.c | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index b8809d4..a68b4a0 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -307,6 +307,13 @@ 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)) @@ -1541,6 +1558,13 @@ struct ctl_table random_table[] = { .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, .maxlen = 16, |
