1 files changed, 148 insertions, 0 deletions
diff --git a/src/libnm-glib-aux/nm-random-utils.c b/src/libnm-glib-aux/nm-random-utils.c
new file mode 100644
index 0000000000..56b99d5e3c
--- /dev/null
+++ b/src/libnm-glib-aux/nm-random-utils.c
@@ -0,0 +1,148 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2017 Red Hat, Inc.
+ */
+
+#include "libnm-glib-aux/nm-default-glib-i18n-lib.h"
+
+#include "nm-random-utils.h"
+
+#include <fcntl.h>
+
+#if USE_SYS_RANDOM_H
+    #include <sys/random.h>
+#else
+    #include <linux/random.h>
+#endif
+
+#include "nm-shared-utils.h"
+
+/*****************************************************************************/
+
+/**
+ * nm_utils_random_bytes:
+ * @p: the buffer to fill
+ * @n: the number of bytes to write to @p.
+ *
+ * Uses getrandom() or reads /dev/urandom to fill the buffer
+ * with random data. If all fails, as last fallback it uses
+ * GRand to fill the buffer with pseudo random numbers.
+ * The function always succeeds in writing some random numbers
+ * to the buffer. The return value of FALSE indicates that the
+ * obtained bytes are probably not of good randomness.
+ *
+ * Returns: whether the written bytes are good. If you
+ * don't require good randomness, you can ignore the return
+ * value.
+ *
+ * Note that if calling getrandom() fails because there is not enough
+ * entropy (at early boot), the function will read /dev/urandom.
+ * Which of course, still has low entropy, and cause kernel to log
+ * a warning.
+ */
+gboolean
+nm_utils_random_bytes(void *p, size_t n)
+{
+    int      fd;
+    int      r;
+    gboolean has_high_quality = TRUE;
+    gboolean urandom_success;
+    guint8 * buf           = p;
+    gboolean avoid_urandom = FALSE;
+
+    g_return_val_if_fail(p, FALSE);
+    g_return_val_if_fail(n > 0, FALSE);
+
+#if HAVE_GETRANDOM
+    {
+        static gboolean have_syscall = TRUE;
+
+        if (have_syscall) {
+            r = getrandom(buf, n, GRND_NONBLOCK);
+            if (r > 0) {
+                if ((size_t) r == n)
+                    return TRUE;
+
+                /* no or partial read. There is not enough entropy.
+                 * Fill the rest reading from urandom, and remember that
+                 * some bits are not high quality. */
+                nm_assert(r < n);
+                buf += r;
+                n -= r;
+                has_high_quality = FALSE;
+
+                /* At this point, we don't want to read /dev/urandom, because
+                 * the entropy pool is low (early boot?), and asking for more
+                 * entropy causes kernel messages to be logged.
+                 *
+                 * We use our fallback via GRand. Note that g_rand_new() also
+                 * tries to seed itself with data from /dev/urandom, but since
+                 * we reuse the instance, it shouldn't matter. */
+                avoid_urandom = TRUE;
+            } else {
+                if (errno == ENOSYS) {
+                    /* no support for getrandom(). We don't know whether
+                     * we urandom will give us good quality. Assume yes. */
+                    have_syscall = FALSE;
+                } else {
+                    /* unknown error. We'll read urandom below, but we don't have
+                     * high-quality randomness. */
+                    has_high_quality = FALSE;
+                }
+            }
+        }
+    }
+#endif
+
+    urandom_success = FALSE;
+    if (!avoid_urandom) {
+fd_open:
+        fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC | O_NOCTTY);
+        if (fd < 0) {
+            r = errno;
+            if (r == EINTR)
+                goto fd_open;
+        } else {
+            r = nm_utils_fd_read_loop_exact(fd, buf, n, TRUE);
+            nm_close(fd);
+            if (r >= 0)
+                urandom_success = TRUE;
+        }
+    }
+
+    if (!urandom_success) {
+        static _nm_thread_local GRand *rand = NULL;
+        gsize                          i;
+        int                            j;
+
+        /* we failed to fill the bytes reading from urandom.
+         * Fill the bits using GRand pseudo random numbers.
+         *
+         * We don't have good quality.
+         */
+        has_high_quality = FALSE;
+
+        if (G_UNLIKELY(!rand))
+            rand = g_rand_new();
+
+        nm_assert(n > 0);
+        i = 0;
+        for (;;) {
+            const union {
+                guint32 v32;
+                guint8  v8[4];
+            } v = {
+                .v32 = g_rand_int(rand),
+            };
+
+            for (j = 0; j < 4;) {
+                buf[i++] = v.v8[j++];
+                if (i >= n)
+                    goto done;
+            }
+        }
+done:;
+    }
+
+    return has_high_quality;
+}