seedrng: restore error check on fsync

Or else security people will never stop nagging us.

function                                             old     new   delta
seedrng_main                                         884     906     +22

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 12 insertions, 9 deletions

diff --git a/miscutils/seedrng.c b/miscutils/seedrng.c
index 8c81835f6..4f2441abc 100644
--- a/miscutils/seedrng.c
+++ b/miscutils/seedrng.c
@@ -134,12 +134,14 @@ static void seed_from_file_if_exists(const char *filename, int dfd, bool credit,
                 /* We are going to use this data to seed the RNG:
                  * we believe it to genuinely containing entropy.
                  * If this just-unlinked file survives
-                 * (e.g. if machine crashes _right now_)
+                 * (if machine crashes before deletion is recorded on disk)
                  * and we reuse it after reboot, this assumption
-                 * would be violated. Fsync the directory to
-                 * make sure file is gone:
+                 * would be violated, and RNG may end up generating
+                 * the same data. fsync the directory
+                 * to make sure file is gone:
                  */
-                fsync(dfd);
+                if (fsync(dfd) != 0)
+                        bb_simple_perror_msg_and_die("I/O error");
 
 //Length is not random, and taking its address spills variable to stack
 //              sha256_hash(hash, &seed_len, sizeof(seed_len));
@@ -210,10 +212,11 @@ int seedrng_main(int argc UNUSED_PARAM, char **argv)
         sha256_hash(&hash, &timestamp, sizeof(timestamp));
 
         for (i = 0; i <= 1; i++) {
-                seed_from_file_if_exists(i == 0 ? NON_CREDITABLE_SEED_NAME : CREDITABLE_SEED_NAME,
-                                        dfd,
-                                        /* credit? */ (opts ^ OPT_n) & i, /* 0, then 1 unless -n */
-                                        &hash);
+                seed_from_file_if_exists(
+                        i == 0 ? NON_CREDITABLE_SEED_NAME : CREDITABLE_SEED_NAME,
+                        dfd,
+                        /*credit?*/ (opts ^ OPT_n) & i, /* 0, then 1 unless -n */
+                        &hash);
         }
 
         new_seed_len = determine_optimal_seed_len();
@@ -224,7 +227,7 @@ int seedrng_main(int argc UNUSED_PARAM, char **argv)
         sha256_end(&hash, new_seed + new_seed_len - SHA256_OUTSIZE);
 
         printf("Saving %u bits of %screditable seed for next boot\n",
-                        (unsigned)new_seed_len * 8, new_seed_creditable ? "" : "non-");
+                (unsigned)new_seed_len * 8, new_seed_creditable ? "" : "non-");
         fd = xopen3(NON_CREDITABLE_SEED_NAME, O_WRONLY | O_CREAT | O_TRUNC, 0400);
         xwrite(fd, new_seed, new_seed_len);
         if (new_seed_creditable) {