[PATCH 1/1] tools: use cryptographically safe RNG

[Heinrich Schuchardt]

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

Fixes: cc34f04efd63 ("tools: image-host.c: use random instead of rand")
Addresses-Coverity-ID: 312953 Calling risky function
Signed-off-by: Heinrich Schuchardt <heinrich.schucha...@canonical.com>
---
 tools/image-host.c | 35 +++--------------------------------
 1 file changed, 3 insertions(+), 32 deletions(-)

diff --git a/tools/image-host.c b/tools/image-host.c
index 5e01b853c50..e24e053825b 100644
--- a/tools/image-host.c
+++ b/tools/image-host.c
@@ -364,36 +364,6 @@ 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)
-{
-       unsigned char *tmp = data;
-       struct timespec date;
-       int i, ret;
-
-       if (!tmp) {
-               fprintf(stderr, "%s: pointer data is NULL\n", __func__);
-               ret = -1;
-               goto out;
-       }
-
-       ret = clock_gettime(CLOCK_MONOTONIC, &date);
-       if (ret) {
-               fprintf(stderr, "%s: clock_gettime has failed (%s)\n", __func__,
-                       strerror(errno));
-               goto out;
-       }
-
-       srandom(date.tv_nsec);
-
-       for (i = 0; i < size; i++) {
-               *tmp = random() & 0xff;
-               tmp++;
-       }
-
- out:
-       return ret;
-}
-
 static int fit_image_setup_cipher(struct image_cipher_info *info,
                                  const char *keydir, void *fit,
                                  const char *image_name, int image_noffset,
@@ -465,8 +435,9 @@ static int fit_image_setup_cipher(struct image_cipher_info 
*info,
                if (ret < 0)
                        goto out;
        } else {
-               /* Generate an ramdom IV */
-               ret = get_random_data((void *)info->iv, info->cipher->iv_len);
+               /* Generate a random IV */
+               arc4random_buf((void *)info->iv, info->cipher->iv_len);
+               ret = 0;
        }
 
  out:
-- 
2.45.2