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Use ioctl RNDADDENTROPY for writing back random seed #4513

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Use ioctl RNDADDENTROPY for writing back random seed #4513

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8df1001
The RNDADDENTROPY ioctl is used to feed back the random entropy
bitstreamout Oct 25, 2016
1b61059
Merge branch 'master' into random
bitstreamout Jan 24, 2017
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44 changes: 37 additions & 7 deletions src/random-seed/random-seed.c
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Expand Up @@ -19,7 +19,9 @@

#include <errno.h>
#include <fcntl.h>
#include <linux/random.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <unistd.h>

Expand All @@ -33,9 +35,35 @@

#define POOL_SIZE_MIN 512

static ssize_t get_random(int fd, struct rand_pool_info **entropy) {
ssize_t len;
int r;

r = ioctl(fd, RNDGETENTCNT, &((*entropy)->entropy_count));
if (r < 0)
return -errno;

len = loop_read(fd, (*entropy)->buf, (*entropy)->buf_size, false);
if (len < 0)
return len;
(*entropy)->buf_size = len;

return sizeof(struct rand_pool_info) + len;
}

static ssize_t put_random(int fd, struct rand_pool_info *entropy) {
int r;

r = ioctl(fd, RNDADDENTROPY, entropy);
if (r < 0)
return -errno;

return 0;
}

int main(int argc, char *argv[]) {
_cleanup_close_ int seed_fd = -1, random_fd = -1;
_cleanup_free_ void* buf = NULL;
_cleanup_free_ struct rand_pool_info *entropy = NULL;
size_t buf_size = 0;
ssize_t k;
int r, open_rw_error;
Expand Down Expand Up @@ -66,11 +94,13 @@ int main(int argc, char *argv[]) {
if (buf_size <= POOL_SIZE_MIN)
buf_size = POOL_SIZE_MIN;

buf = malloc(buf_size);
if (!buf) {
entropy = malloc(sizeof(struct rand_pool_info) + buf_size);
if (!entropy) {
r = log_oom();
goto finish;
}
entropy->buf_size = buf_size;
buf_size += sizeof(struct rand_pool_info);

r = mkdir_parents_label(RANDOM_SEED, 0755);
if (r < 0) {
Expand Down Expand Up @@ -113,7 +143,7 @@ int main(int argc, char *argv[]) {
}
}

k = loop_read(seed_fd, buf, buf_size, false);
k = loop_read(seed_fd, entropy, buf_size, false);
if (k < 0)
r = log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m");
else if (k == 0) {
Expand All @@ -122,7 +152,7 @@ int main(int argc, char *argv[]) {
} else {
(void) lseek(seed_fd, 0, SEEK_SET);

r = loop_write(random_fd, buf, (size_t) k, false);
r = put_random(random_fd, entropy);
if (r < 0)
log_error_errno(r, "Failed to write seed to /dev/urandom: %m");
}
Expand Down Expand Up @@ -155,7 +185,7 @@ int main(int argc, char *argv[]) {
(void) fchmod(seed_fd, 0600);
(void) fchown(seed_fd, 0, 0);

k = loop_read(random_fd, buf, buf_size, false);
k = get_random(random_fd, &entropy);
if (k < 0) {
r = log_error_errno(k, "Failed to read new seed from /dev/urandom: %m");
goto finish;
Expand All @@ -166,7 +196,7 @@ int main(int argc, char *argv[]) {
goto finish;
}

r = loop_write(seed_fd, buf, (size_t) k, false);
r = loop_write(seed_fd, entropy, k, false);
if (r < 0)
log_error_errno(r, "Failed to write new random seed file: %m");
}
Expand Down