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seedrng: re-add fsync after unlink, and explain its purpose

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function                                             old     new   delta
seedrng_main                                        1003    1022     +19

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2022-04-30 23:17:58 +02:00
parent 267178c628
commit 4648754119
1 changed files with 12 additions and 1 deletions
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13
util-linux/seedrng.c
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@ -128,7 +128,7 @@ static void seed_rng(uint8_t *seed, size_t len, bool credit)
close(random_fd); 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]; uint8_t seed[MAX_SEED_LEN];
ssize_t 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); xunlink(filename);
if (seed_len != 0) { 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_len, sizeof(seed_len));
sha256_hash(hash, seed, seed_len); sha256_hash(hash, seed, seed_len);
printf("Seeding %u bits %s crediting\n", 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) { for (int i = 1; i < 3; ++i) {
seed_from_file_if_exists(i == 1 ? NON_CREDITABLE_SEED_NAME : CREDITABLE_SEED_NAME, seed_from_file_if_exists(i == 1 ? NON_CREDITABLE_SEED_NAME : CREDITABLE_SEED_NAME,
dfd,
i == 1 ? false : !skip_credit, i == 1 ? false : !skip_credit,
&hash); &hash);
} }