464875411
Denys Vlasenko
2022-04-30
Subject
seedrng: re-add fsync after unlink, and explain its purpose
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Commit Diff GitHub →
util-linux/seedrng.c+12 -1
| @@ -128,7 +128,7 @@ static void seed_rng(uint8_t *seed, size_t len, bool credit) | |
| close(random_fd); | |
| } | |
| - | static void seed_from_file_if_exists(const char *filename, bool credit, sha256_ctx_t *hash) |
| + | static void seed_from_file_if_exists(const char *filename, int dfd, bool credit, sha256_ctx_t *hash) |
| { | |
| uint8_t seed[MAX_SEED_LEN]; | |
| ssize_t seed_len; | |
| @@ -141,6 +141,16 @@ static void seed_from_file_if_exists(const char *filename, bool credit, sha256_c | |
| } | |
| xunlink(filename); | |
| if (seed_len != 0) { | |
| + | /* 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_) |
| + | * and we reuse it after reboot, this assumption |
| + | * would be violated. Fsync the directory to |
| + | * make sure file is gone: |
| + | */ |
| + | fsync(dfd); |
| + | |
| sha256_hash(hash, &seed_len, sizeof(seed_len)); | |
| sha256_hash(hash, seed, seed_len); | |
| printf("Seeding %u bits %s crediting\n", | |
| @@ -193,6 +203,7 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[]) | |
| for (int i = 1; i < 3; ++i) { | |
| seed_from_file_if_exists(i == 1 ? NON_CREDITABLE_SEED_NAME : CREDITABLE_SEED_NAME, | |
| + | dfd, |
| i == 1 ? false : !skip_credit, | |
| &hash); | |
| } | |