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seedrng: do not hash lengths, they are very predictable

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function                                             old     new   delta
seedrng_main                                         982     930     -52

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2022-05-01 02:06:20 +02:00
parent fb4546c7af
commit 7471658038
1 changed files with 5 additions and 3 deletions
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8
util-linux/seedrng.c
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@ -151,7 +151,8 @@ static void seed_from_file_if_exists(const char *filename, int dfd, bool credit,
*/ */
fsync(dfd); 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); sha256_hash(hash, seed, seed_len);
printf("Seeding %u bits %s crediting\n", printf("Seeding %u bits %s crediting\n",
(unsigned)seed_len * 8, credit ? "and" : "without"); (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_len = determine_optimal_seed_len();
new_seed_creditable = read_new_seed(new_seed, new_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_hash(&hash, new_seed, new_seed_len);
sha256_end(&hash, new_seed + new_seed_len - SHA256_OUTSIZE); 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); xwrite(fd, new_seed, new_seed_len);
if (new_seed_creditable) { if (new_seed_creditable) {
/* More paranoia when we create a file which we believe contains /* 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) if (fsync(fd) < 0)
bb_perror_msg_and_die("can't write '%s'", NON_CREDITABLE_SEED_NAME); bb_perror_msg_and_die("can't write '%s'", NON_CREDITABLE_SEED_NAME);