[3/4] batctl: Add helper to generate instant random bytes
Commit Message
Linux provides different ways to get instant random bytes. These are not
all supported on all systems and thus a fallback may have to be used.
Abstract all this in a single function which can be used from different
parts of the code.
The current implementations are
* get random data from urandom pool via SYS_getrandom syscall
* get random data from reading /dev/urandom
* fallback to per-program prng initialized via the current time (seconds +
nanoseconds)
All are tried in this order in hope to get a high quality random number
source before falling back to some really low quality one.
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
functions.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
functions.h | 2 ++
2 files changed, 67 insertions(+)
@@ -41,6 +41,7 @@
#include <linux/if_link.h>
#include <linux/rtnetlink.h>
#include <linux/neighbour.h>
+#include <sys/syscall.h>
#include <errno.h>
#include <net/if.h>
#include <netlink/socket.h>
@@ -1071,3 +1072,67 @@ int check_mesh_iface_ownership(char *mesh_iface, char *hard_iface)
return EXIT_SUCCESS;
}
+
+static int get_random_bytes_syscall(void *buf __unused, size_t buflen __unused)
+{
+#ifdef SYS_getrandom
+ return syscall(SYS_getrandom, buf, buflen, 0);
+#else
+ return -EOPNOTSUPP;
+#endif
+}
+
+static int get_random_bytes_urandom(void *buf, size_t buflen)
+{
+ int fd;
+ ssize_t r;
+
+ fd = open("/dev/urandom", O_RDONLY);
+ if (fd < 0)
+ return -EOPNOTSUPP;
+
+ r = read(fd, buf, buflen);
+ close(fd);
+ if (r < 0)
+ return -EOPNOTSUPP;
+
+ if ((size_t)r != buflen)
+ return -EOPNOTSUPP;
+
+ return 0;
+}
+
+static int get_random_bytes_fallback(void *buf, size_t buflen)
+{
+ struct timespec now;
+ static int initialized = 0;
+ size_t i;
+ uint8_t *bufc = buf;
+
+ /* this is not a good source for randomness */
+ if (!initialized) {
+ clock_gettime(CLOCK_MONOTONIC, &now);
+ srand(now.tv_sec ^ now.tv_nsec);
+ initialized = 1;
+ }
+
+ for (i = 0; i < buflen; i++)
+ bufc[i] = rand() & 0xff;
+
+ return 0;
+}
+
+void get_random_bytes(void *buf, size_t buflen)
+{
+ int ret;
+
+ ret = get_random_bytes_syscall(buf, buflen);
+ if (ret != -EOPNOTSUPP)
+ return;
+
+ ret = get_random_bytes_urandom(buf, buflen);
+ if (ret != -EOPNOTSUPP)
+ return;
+
+ get_random_bytes_fallback(buf, buflen);
+}
@@ -53,6 +53,8 @@ int netlink_simple_request(struct nl_msg *msg);
int check_mesh_iface(char *mesh_iface);
int check_mesh_iface_ownership(char *mesh_iface, char *hard_iface);
+void get_random_bytes(void *buf, size_t buflen);
+
int print_routing_algos(void);
extern char *line_ptr;