3bfbcb580
Denys Vlasenko
2022-05-02
Subject
seedrng: restore error check on fsync
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miscutils/seedrng.c+12 -9
| @@ -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, ×tamp, 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) { | |