seedrng: re-add fsync after unlink, and explain its purpose
function old new delta
seedrng_main 1003 1022 +19
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/util-linux/seedrng.c b/util-linux/seedrng.c
index 74bf633..b79ce66 100644
--- a/util-linux/seedrng.c
+++ b/util-linux/seedrng.c
@@ -128,7 +128,7 @@
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 @@
}
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 @@
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);
}