diff options
Diffstat (limited to 'shared/nm-glib-aux/nm-random-utils.c')
| -rw-r--r-- | shared/nm-glib-aux/nm-random-utils.c | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/shared/nm-glib-aux/nm-random-utils.c b/shared/nm-glib-aux/nm-random-utils.c new file mode 100644 index 0000000000..d7c7da4221 --- /dev/null +++ b/shared/nm-glib-aux/nm-random-utils.c @@ -0,0 +1,165 @@ +/* -*- Mode: C; tab-width: 4; indent-tabs-mode: t; c-basic-offset: 4 -*- */ +/* NetworkManager -- Network link manager + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2 of the License, or (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library; if not, write to the + * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, + * Boston, MA 02110-1301 USA. + * + * (C) Copyright 2017 Red Hat, Inc. + */ + +#include "nm-default.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; +} |