747165803
Denys Vlasenko
2022-05-01
Subject
seedrng: do not hash lengths, they are very predictable
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util-linux/seedrng.c+5 -3
| @@ -151,7 +151,8 @@ static void seed_from_file_if_exists(const char *filename, int dfd, bool credit, | |
| */ | |
| fsync(dfd); | |
| - | sha256_hash(hash, &seed_len, sizeof(seed_len)); |
| + | //Length is not random, and taking its address spills variable to stack |
| + | // sha256_hash(hash, &seed_len, sizeof(seed_len)); |
| sha256_hash(hash, seed, seed_len); | |
| printf("Seeding %u bits %s crediting\n", | |
| (unsigned)seed_len * 8, credit ? "and" : "without"); | |
| @@ -220,7 +221,8 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[]) | |
| new_seed_len = determine_optimal_seed_len(); | |
| new_seed_creditable = read_new_seed(new_seed, new_seed_len); | |
| - | sha256_hash(&hash, &new_seed_len, sizeof(new_seed_len)); |
| + | //Length is not random, and taking its address spills variable to stack |
| + | // sha256_hash(&hash, &new_seed_len, sizeof(new_seed_len)); |
| sha256_hash(&hash, new_seed, new_seed_len); | |
| sha256_end(&hash, new_seed + new_seed_len - SHA256_OUTSIZE); | |
| @@ -230,7 +232,7 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[]) | |
| xwrite(fd, new_seed, new_seed_len); | |
| if (new_seed_creditable) { | |
| /* More paranoia when we create a file which we believe contains | |
| - | * genuine entropy: make sure disk is not full, quota was't esceeded, etc: |
| + | * genuine entropy: make sure disk is not full, quota was't exceeded, etc: |
| */ | |
| if (fsync(fd) < 0) | |
| bb_perror_msg_and_die("can't write '%s'", NON_CREDITABLE_SEED_NAME); | |