seedrng: simplify read_new_seed() to not have error return

gcc in fact detects this and does this transformation
when generating code - no object code changes.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 17 insertions, 14 deletions

diff --git a/util-linux/seedrng.c b/util-linux/seedrng.c
index 3f4c5c0c8..5559ba77c 100644
--- a/util-linux/seedrng.c
+++ b/util-linux/seedrng.c
@@ -75,31 +75,38 @@ static size_t determine_optimal_seed_len(void)
         return MAX(MIN(poolsize, MAX_SEED_LEN), MIN_SEED_LEN);
 }
 
-static int read_new_seed(uint8_t *seed, size_t len, bool *is_creditable)
+static bool read_new_seed(uint8_t *seed, size_t len)
 {
+        bool is_creditable;
         ssize_t ret;
 
         ret = getrandom(seed, len, GRND_NONBLOCK);
         if (ret == (ssize_t)len) {
-                *is_creditable = true;
-                return 0;
+                return true;
         }
         if (ret < 0 && errno == ENOSYS) {
                 struct pollfd random_fd = {
                         .fd = xopen("/dev/random", O_RDONLY),
                         .events = POLLIN
                 };
-                *is_creditable = poll(&random_fd, 1, 0) == 1;
+                is_creditable = poll(&random_fd, 1, 0) == 1;
+//This is racy. is_creditable can be set to true here, but other process
+//can consume "good" random data from /dev/urandom before we do it below.
                 close(random_fd.fd);
         } else {
-                *is_creditable = false;
                 if (getrandom(seed, len, GRND_INSECURE) == (ssize_t)len)
-                        return 0;
+                        return false;
+                is_creditable = false;
         }
+
+        /* Either getrandom() is not implemented, or
+         * getrandom(GRND_INSECURE) did not give us LEN bytes.
+         * Fallback to reading /dev/urandom.
+         */
         errno = 0;
         if (open_read_close("/dev/urandom", seed, len) != (ssize_t)len)
                 bb_perror_msg_and_die("can't read '%s'", "/dev/urandom");
-        return 0;
+        return is_creditable;
 }
 
 static void seed_rng(uint8_t *seed, size_t len, bool credit)
@@ -190,17 +197,13 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[])
         }
 
         new_seed_len = determine_optimal_seed_len();
-        if (read_new_seed(new_seed, new_seed_len, &new_seed_creditable) < 0) {
-                bb_perror_msg("can't%s seed", " read new");
-                new_seed_len = SHA256_OUTSIZE;
-                memset(new_seed, 0, SHA256_OUTSIZE);
-                program_ret |= 1 << 3;
-        }
+        new_seed_creditable = read_new_seed(new_seed, new_seed_len);
         sha256_hash(&hash, &new_seed_len, sizeof(new_seed_len));
         sha256_hash(&hash, new_seed, new_seed_len);
         sha256_end(&hash, new_seed + new_seed_len - SHA256_OUTSIZE);
 
-        printf("Saving %u bits of %screditable seed for next boot\n", (unsigned)new_seed_len * 8, new_seed_creditable ? "" : "non-");
+        printf("Saving %u bits of %screditable seed for next boot\n",
+                        (unsigned)new_seed_len * 8, new_seed_creditable ? "" : "non-");
         fd = open(NON_CREDITABLE_SEED_NAME, O_WRONLY | O_CREAT | O_TRUNC, 0400);
         if (fd < 0 || full_write(fd, new_seed, new_seed_len) != (ssize_t)new_seed_len || fsync(fd) < 0) {
                 bb_perror_msg("can't%s seed", " write");