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tools: use cryptographically safe RNG

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The PRNG implementing the random() function only has 2^31 states and
therefore is unsafe to use for cryptography. Use arc4random() instead.

Fixes: cc34f04efd ("tools: image-host.c: use random instead of rand")
Addresses-Coverity-ID: 312953 Calling risky function
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
This commit is contained in:
Heinrich Schuchardt 2025-02-11 14:55:22 +01:00 • committed by Tom Rini
parent e93f11148a
commit 50e8089c1d
1 changed files with 34 additions and 21 deletions
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55
tools/image-host.c
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@ -364,33 +364,46 @@ static int fit_image_read_key_iv_data(const char *keydir, const char *key_iv_nam
return ret;
}
static int get_random_data(void *data, int size)
/**
* get_random_data() - fill buffer with random data
*
* There is no common cryptographically safe function in Linux and BSD.
* Hence directly access the /dev/urandom PRNG.
*
* @data: buffer to fill
* @size: buffer size
*/
static int get_random_data(void *data, size_t size)
{
unsigned char *tmp = data;
struct timespec date;
int i, ret;
int fd;
int ret;
if (!tmp) {
fprintf(stderr, "%s: pointer data is NULL\n", __func__);
ret = -1;
goto out;
fd = open("/dev/urandom", O_RDONLY);
if (fd < 0) {
perror("Failed to open /dev/urandom");
return -1;
}
ret = clock_gettime(CLOCK_MONOTONIC, &date);
if (ret) {
fprintf(stderr, "%s: clock_gettime has failed (%s)\n", __func__,
strerror(errno));
goto out;
while (size) {
ssize_t count;
count = read(fd, data, size);
if (count < 0) {
if (errno == EINTR) {
continue;
} else {
perror("Failed to read from /dev/urandom");
ret = -1;
goto out;
}
}
data += count;
size -= count;
}
ret = 0;
out:
close(fd);
srandom(date.tv_nsec);
for (i = 0; i < size; i++) {
*tmp = random() & 0xff;
tmp++;
}
out:
return ret;
}