[PATCH v2] Add getrandom syscall wrapper and getentropy function

[Hauke Mehrtens <hauke@hauke-m.de>]

This syscall is available since Linux 3.17 and was also implemented in
glibc in version 2.25 using the same interfaces.
The getrandom function is a pure syscall wrapper liker glibc does it.
getentropy is implemented on top of the getrandom syscall and fills the
buffer.

Currently no fallback is implemented this could be possible by using
AT_RANDOM in the future.
---
 include/sys/random.h   | 21 +++++++++++++++++++++
 src/linux/getentropy.c | 29 +++++++++++++++++++++++++++++
 src/linux/getrandom.c  |  7 +++++++
 3 files changed, 57 insertions(+)
 create mode 100644 include/sys/random.h
 create mode 100644 src/linux/getentropy.c
 create mode 100644 src/linux/getrandom.c

diff --git a/include/sys/random.h b/include/sys/random.h
new file mode 100644
index 00000000..5b09e394
--- /dev/null
+++ b/include/sys/random.h
@@ -0,0 +1,21 @@
+#ifndef _SYS_RANDOM_H
+#define _SYS_RANDOM_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define __NEED_size_t
+#define __NEED_ssize_t
+#include <bits/alltypes.h>
+
+#define GRND_NONBLOCK	0x0001
+#define GRND_RANDOM	0x0002
+
+ssize_t getrandom(void *buf, size_t buflen, unsigned int flags);
+
+int getentropy(void *buffer, size_t length);
+
+#ifdef __cplusplus
+}
+#endif
+#endif
diff --git a/src/linux/getentropy.c b/src/linux/getentropy.c
new file mode 100644
index 00000000..48ca3d51
--- /dev/null
+++ b/src/linux/getentropy.c
@@ -0,0 +1,29 @@
+#include <sys/random.h>
+#include <errno.h>
+#include "syscall.h"
+
+int getentropy(void *buffer, size_t length)
+{
+	int ret;
+	char *pos = buffer;
+	size_t rem = length;
+
+	if (length > 256) {
+		return __syscall_ret(-EIO);
+	}
+
+	while (rem) {
+		ret = __syscall_cp(SYS_getrandom, pos, rem, 0);
+		if (ret == -EINTR) {
+			continue;
+		} else if (ret == -EFAULT || ret == -ENOSYS) {
+			return __syscall_ret(ret);
+		} else if (ret <= 0) {
+			return __syscall_ret(-EIO);
+		}
+
+		pos += ret;
+		rem -= ret;
+	}
+	return 0;
+}
diff --git a/src/linux/getrandom.c b/src/linux/getrandom.c
new file mode 100644
index 00000000..795b932c
--- /dev/null
+++ b/src/linux/getrandom.c
@@ -0,0 +1,7 @@
+#include <sys/random.h>
+#include "syscall.h"
+
+ssize_t getrandom(void *buf, size_t buflen, unsigned int flags)
+{
+	return syscall_cp(SYS_getrandom, buf, buflen, flags);
+}
-- 
2.11.0