seedrng: do not hash lengths, they are very predictable
function old new delta seedrng_main 982 930 -52 Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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@ -151,7 +151,8 @@ static void seed_from_file_if_exists(const char *filename, int dfd, bool credit,
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*/
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fsync(dfd);
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sha256_hash(hash, &seed_len, sizeof(seed_len));
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//Length is not random, and taking its address spills variable to stack
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// sha256_hash(hash, &seed_len, sizeof(seed_len));
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sha256_hash(hash, seed, seed_len);
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printf("Seeding %u bits %s crediting\n",
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(unsigned)seed_len * 8, credit ? "and" : "without");
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@ -220,7 +221,8 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[])
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new_seed_len = determine_optimal_seed_len();
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new_seed_creditable = read_new_seed(new_seed, new_seed_len);
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sha256_hash(&hash, &new_seed_len, sizeof(new_seed_len));
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//Length is not random, and taking its address spills variable to stack
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// sha256_hash(&hash, &new_seed_len, sizeof(new_seed_len));
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sha256_hash(&hash, new_seed, new_seed_len);
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sha256_end(&hash, new_seed + new_seed_len - SHA256_OUTSIZE);
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@ -230,7 +232,7 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[])
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xwrite(fd, new_seed, new_seed_len);
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if (new_seed_creditable) {
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/* More paranoia when we create a file which we believe contains
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* genuine entropy: make sure disk is not full, quota was't esceeded, etc:
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* genuine entropy: make sure disk is not full, quota was't exceeded, etc:
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*/
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if (fsync(fd) < 0)
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bb_perror_msg_and_die("can't write '%s'", NON_CREDITABLE_SEED_NAME);
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