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plugins/urandom: use RNDADDENTROPY ioctl to seed kernel rng

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This patch switches from "cp /var/lib/misc/random-seed /dev/urandom"
to use the kernel RNDADDENTROPY ioctl, which actually increments the
entropy count.

Also, the amount of random data saved at reboot is increased from the
fairly low 512 to 32768 bytes.

All in all, this should greatly improve the stability of most systems
during, or close to, bootstrap.  In particular embedded systems with
limited or no HWRNG.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
This commit is contained in:
Joachim Wiberg
2022-01-02 01:04:07 +01:00
parent 621d95a89e
commit 615cd5aac3
1 changed files with 64 additions and 2 deletions
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plugins/urandom.c
+64 -2
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@@ -22,6 +22,7 @@
*/
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/time.h> /* gettimeofday() */
#include <sys/types.h>
@@ -30,15 +31,25 @@
#else
# include <lite/lite.h>
#endif
#include <linux/random.h>
#include "config.h"
#include "finit.h"
#include "helpers.h"
#include "plugin.h"
#ifndef RANDOM_BYTES
#define RANDOM_BYTES (32*1024)
#endif
static void setup(void *arg)
{
#ifdef RANDOMSEED
struct rand_pool_info *rpi;
ssize_t len = 0;
int rc = -1;
int fd, err;
if (rescue) {
_d("Skipping %s plugin in rescue mode.", __FILE__);
return;
@@ -71,7 +82,58 @@ static void setup(void *arg)
}
print_desc("Initializing random number generator", NULL);
print_result(512 != copyfile(RANDOMSEED, "/dev/urandom", 0, 0));
/*
* Simply copying our saved entropy to /dev/urandom doesn't
* increment the kernel "entropy count", instead we must use
* the ioctl below.
*/
fd = open(RANDOMSEED, O_RDONLY);
if (fd < 0)
goto fallback;
rpi = malloc(sizeof(*rpi) + RANDOM_BYTES);
if (!rpi) {
close(fd);
goto fallback;
}
do {
ssize_t num;
num = read(fd, &rpi->buf[len], RANDOM_BYTES - len);
if (num <= 0) {
if (num == -1 && errno == EINTR)
continue;
if (len > 0)
break;
free(rpi);
goto fallback;
}
len += num;
} while (len < RANDOM_BYTES);
close(fd);
fd = open("/dev/urandom", O_WRONLY);
if (fd < 0) {
free(rpi);
goto fallback;
}
rpi->buf_size = len;
rpi->entropy_count = len * 8;
rc = ioctl(fd, RNDADDENTROPY, rpi);
err = errno;
close(fd);
free(rpi);
if (rc < 0)
logit(LOG_ERR, "Failed adding entropy to kernel random pool: %s", strerror(err));
print_result(rc < 0);
return;
fallback:
print_result(512 > copyfile(RANDOMSEED, "/dev/urandom", 0, 0));
#endif
}
@@ -88,7 +150,7 @@ static void save(void *arg)
prev = umask(077);
print_desc("Saving random seed", NULL);
print_result(512 != copyfile("/dev/urandom", RANDOMSEED, 512, 0));
print_result(RANDOM_BYTES != copyfile("/dev/urandom", RANDOMSEED, RANDOM_BYTES, 0));
umask(prev);
#endif