diff options
Diffstat (limited to 'src/random-seed/random-seed.c')
| -rw-r--r-- | src/random-seed/random-seed.c | 26 |
1 files changed, 25 insertions, 1 deletions
diff --git a/src/random-seed/random-seed.c b/src/random-seed/random-seed.c index 7724e0365e..bba8335720 100644 --- a/src/random-seed/random-seed.c +++ b/src/random-seed/random-seed.c @@ -26,6 +26,7 @@ #include "random-util.h" #include "string-util.h" #include "sync-util.h" +#include "sha256.h" #include "util.h" #include "xattr-util.h" @@ -106,9 +107,11 @@ static int run(int argc, char *argv[]) { _cleanup_close_ int seed_fd = -1, random_fd = -1; bool read_seed_file, write_seed_file, synchronous; _cleanup_free_ void* buf = NULL; + struct sha256_ctx hash_state; + uint8_t hash[32]; size_t buf_size; struct stat st; - ssize_t k; + ssize_t k, l; int r; log_setup(); @@ -242,6 +245,16 @@ static int run(int argc, char *argv[]) { if (r < 0) log_error_errno(r, "Failed to write seed to /dev/urandom: %m"); } + /* If we're going to later write out a seed file, initialize a hash state with + * the contents of the seed file we just read, so that the new one can't regress + * in entropy. */ + if (write_seed_file) { + sha256_init_ctx(&hash_state); + if (k < 0) + k = 0; + sha256_process_bytes(&k, sizeof(k), &hash_state); + sha256_process_bytes(buf, k, &hash_state); + } } if (write_seed_file) { @@ -277,6 +290,17 @@ static int run(int argc, char *argv[]) { "Got EOF while reading from /dev/urandom."); } + /* If we previously read in a seed file, then hash the new seed into the old one, + * and replace the last 32 bytes of the seed with the hash output, so that the + * new seed file can't regress in entropy. */ + if (read_seed_file) { + sha256_process_bytes(&k, sizeof(k), &hash_state); + sha256_process_bytes(buf, k, &hash_state); + sha256_finish_ctx(&hash_state, hash); + l = MIN(k, 32); + memcpy((uint8_t *)buf + k - l, hash, l); + } + r = loop_write(seed_fd, buf, (size_t) k, false); if (r < 0) return log_error_errno(r, "Failed to write new random seed file: %m"); |