chiark / gitweb /
util: unify how we see srand()
[elogind.git] / src / shared / util.c
index 4143f6d..0f44eb5 100644 (file)
@@ -2466,14 +2466,53 @@ char* dirname_malloc(const char *path) {
 }
 
 int dev_urandom(void *p, size_t n) {
-        _cleanup_close_ int fd;
+        static int have_syscall = -1;
+        int r, fd;
         ssize_t k;
 
+        /* Gathers some randomness from the kernel. This call will
+         * never block, and will always return some data from the
+         * kernel, regardless if the random pool is fully initialized
+         * or not. It thus makes no guarantee for the quality of the
+         * returned entropy, but is good enough for or usual usecases
+         * of seeding the hash functions for hashtable */
+
+        /* Use the getrandom() syscall unless we know we don't have
+         * it, or when the requested size is too large for it. */
+        if (have_syscall != 0 || (size_t) (int) n != n) {
+                r = getrandom(p, n, GRND_NONBLOCK);
+                if (r == (int) n) {
+                        have_syscall = true;
+                        return 0;
+                }
+
+                if (r < 0) {
+                        if (errno == ENOSYS)
+                                /* we lack the syscall, continue with
+                                 * reading from /dev/urandom */
+                                have_syscall = false;
+                        else if (errno == EAGAIN)
+                                /* not enough entropy for now. Let's
+                                 * remember to use the syscall the
+                                 * next time, again, but also read
+                                 * from /dev/urandom for now, which
+                                 * doesn't care about the current
+                                 * amount of entropy.  */
+                                have_syscall = true;
+                        else
+                                return -errno;
+                } else
+                        /* too short read? */
+                        return -EIO;
+        }
+
         fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
         if (fd < 0)
                 return errno == ENOENT ? -ENOSYS : -errno;
 
         k = loop_read(fd, p, n, true);
+        safe_close(fd);
+
         if (k < 0)
                 return (int) k;
         if ((size_t) k != n)
@@ -2482,8 +2521,36 @@ int dev_urandom(void *p, size_t n) {
         return 0;
 }
 
-void random_bytes(void *p, size_t n) {
+void initialize_srand(void) {
         static bool srand_called = false;
+        unsigned x;
+#ifdef HAVE_SYS_AUXV_H
+        void *auxv;
+#endif
+
+        if (srand_called)
+                return;
+
+        x = 0;
+
+#ifdef HAVE_SYS_AUXV_H
+        /* The kernel provides us with a bit of entropy in auxv, so
+         * let's try to make use of that to seed the pseudo-random
+         * generator. It's better than nothing... */
+
+        auxv = (void*) getauxval(AT_RANDOM);
+        if (auxv)
+                x ^= *(unsigned*) auxv;
+#endif
+
+        x ^= (unsigned) now(CLOCK_REALTIME);
+        x ^= (unsigned) gettid();
+
+        srand(x);
+        srand_called = true;
+}
+
+void random_bytes(void *p, size_t n) {
         uint8_t *q;
         int r;
 
@@ -2494,28 +2561,7 @@ void random_bytes(void *p, size_t n) {
         /* If some idiot made /dev/urandom unavailable to us, he'll
          * get a PRNG instead. */
 
-        if (!srand_called) {
-                unsigned x = 0;
-
-#ifdef HAVE_SYS_AUXV_H
-                /* The kernel provides us with a bit of entropy in
-                 * auxv, so let's try to make use of that to seed the
-                 * pseudo-random generator. It's better than
-                 * nothing... */
-
-                void *auxv;
-
-                auxv = (void*) getauxval(AT_RANDOM);
-                if (auxv)
-                        x ^= *(unsigned*) auxv;
-#endif
-
-                x ^= (unsigned) now(CLOCK_REALTIME);
-                x ^= (unsigned) gettid();
-
-                srand(x);
-                srand_called = true;
-        }
+        initialize_srand();
 
         for (q = p; q < (uint8_t*) p + n; q ++)
                 *q = rand();