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seedrng: restore error check on fsync

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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>
This commit is contained in:
Denys Vlasenko 2022-05-02 15:03:32 +02:00
parent 5ba56e8b95
commit 3bfbcb5807
1 changed files with 12 additions and 9 deletions
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21
miscutils/seedrng.c
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@ -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) {