arc4random: replace sysctl() with getrandom (on linux)

Since sysctl() is deprecated for a long-long time, according to
sysctl(2):

    Since Linux 2.6.24, uses of this system call result in warnings in the kernel log.

Fixes: libevent#890
Suggested-by: Pierce Lopez

CMakeLists.txt

@@ -365,6 +365,11 @@ if(EVENT__HAVE_SYS_SOCKET_H)
     list(APPEND CMAKE_EXTRA_INCLUDE_FILES sys/socket.h)
 endif()
 
+CHECK_INCLUDE_FILE(sys/random.h EVENT__HAVE_SYS_RANDOM_H)
+if(EVENT__HAVE_SYS_RANDOM_H)
+    list(APPEND CMAKE_EXTRA_INCLUDE_FILES sys/random.h)
+endif()
+
 CHECK_INCLUDE_FILE(netinet/in.h EVENT__HAVE_NETINET_IN_H)
 if(EVENT__HAVE_NETINET_IN_H)
     list(APPEND CMAKE_EXTRA_INCLUDE_FILES netinet/in.h)
@@ -559,9 +564,8 @@ CHECK_SYMBOL_EXISTS("__FUNCTION__" "" EVENT__HAVE___FUNCTION__)
 CHECK_SYMBOL_EXISTS(TAILQ_FOREACH sys/queue.h EVENT__HAVE_TAILQFOREACH)
 CHECK_CONST_EXISTS(CTL_KERN sys/sysctl.h EVENT__HAVE_DECL_CTL_KERN)
 CHECK_CONST_EXISTS(KERN_ARND sys/sysctl.h EVENT__HAVE_DECL_KERN_ARND)
-CHECK_CONST_EXISTS(KERN_RANDOM sys/sysctl.h EVENT__HAVE_DECL_KERN_RANDOM)
-CHECK_CONST_EXISTS(RANDOM_UUID sys/sysctl.h EVENT__HAVE_DECL_RANDOM_UUID)
 CHECK_SYMBOL_EXISTS(F_SETFD fcntl.h EVENT__HAVE_SETFD)
+CHECK_FUNCTION_EXISTS_EX(getrandom EVENT__HAVE_GETRANDOM)
 
 CHECK_TYPE_SIZE(fd_mask EVENT__HAVE_FD_MASK)
 

arc4random.c

@@ -63,6 +63,9 @@
 #ifdef EVENT__HAVE_SYS_SYSCTL_H
 #include <sys/sysctl.h>
 #endif
+#ifdef EVENT__HAVE_SYS_RANDOM_H
+#include <sys/random.h>
+#endif
 #endif
 #include <limits.h>
 #include <stdlib.h>
@@ -167,17 +170,11 @@ arc4_seed_win32(void)
 }
 #endif
 
-#if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL)
-#if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_RANDOM && EVENT__HAVE_DECL_RANDOM_UUID
-#define TRY_SEED_SYSCTL_LINUX
+#if defined(EVENT__HAVE_GETRANDOM)
+#define TRY_SEED_GETRANDOM
 static int
-arc4_seed_sysctl_linux(void)
+arc4_seed_getrandom(void)
 {
-	/* Based on code by William Ahern, this function tries to use the
-	 * RANDOM_UUID sysctl to get entropy from the kernel.  This can work
-	 * even if /dev/urandom is inaccessible for some reason (e.g., we're
-	 * running in a chroot). */
-	int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
 	unsigned char buf[ADD_ENTROPY];
 	size_t len, n;
 	unsigned i;
@@ -188,7 +185,7 @@ arc4_seed_sysctl_linux(void)
 	for (len = 0; len < sizeof(buf); len += n) {
 		n = sizeof(buf) - len;
 
-		if (0 != sysctl(mib, 3, &buf[len], &n, NULL, 0))
+		if (0 == getrandom(&buf[len], n, 0))
 			return -1;
 	}
 	/* make sure that the buffer actually got set. */
@@ -202,8 +199,9 @@ arc4_seed_sysctl_linux(void)
 	evutil_memclear_(buf, sizeof(buf));
 	return 0;
 }
-#endif
+#endif /* EVENT__HAVE_GETRANDOM */
 
+#if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL)
 #if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_ARND
 #define TRY_SEED_SYSCTL_BSD
 static int
@@ -342,6 +340,10 @@ arc4_seed(void)
 	if (0 == arc4_seed_win32())
 		ok = 1;
 #endif
+#ifdef TRY_SEED_GETRANDOM
+	if (0 == arc4_seed_getrandom())
+		ok = 1;
+#endif
 #ifdef TRY_SEED_URANDOM
 	if (0 == arc4_seed_urandom())
 		ok = 1;
@@ -351,12 +353,6 @@ arc4_seed(void)
 	    0 == arc4_seed_proc_sys_kernel_random_uuid())
 		ok = 1;
 #endif
-#ifdef TRY_SEED_SYSCTL_LINUX
-	/* Apparently Linux is deprecating sysctl, and spewing warning
-	 * messages when you try to use it. */
-	if (!ok && 0 == arc4_seed_sysctl_linux())
-		ok = 1;
-#endif
 #ifdef TRY_SEED_SYSCTL_BSD
 	if (0 == arc4_seed_sysctl_bsd())
 		ok = 1;

configure.ac

@@ -248,6 +248,7 @@ AC_CHECK_HEADERS([ \
   sys/timerfd.h \
   sys/uio.h \
   sys/wait.h \
+  sys/random.h \
   errno.h \
 ])
 
@@ -256,6 +257,7 @@ AC_CHECK_HEADERS(sys/sysctl.h, [], [], [
 #include <sys/param.h>
 #endif
 ])
+
 if test "x$ac_cv_header_sys_queue_h" = "xyes"; then
 	AC_MSG_CHECKING(for TAILQ_FOREACH in sys/queue.h)
 	AC_EGREP_CPP(yes,
@@ -328,7 +330,7 @@ if test "x$ac_cv_header_sys_time_h" = "xyes"; then
 fi
 
 if test "x$ac_cv_header_sys_sysctl_h" = "xyes"; then
-	AC_CHECK_DECLS([CTL_KERN, KERN_RANDOM, RANDOM_UUID, KERN_ARND], [], [],
+	AC_CHECK_DECLS([CTL_KERN, KERN_ARND], [], [],
 	   [[#include <sys/types.h>
 	     #include <sys/sysctl.h>]]
 	)
@@ -390,6 +392,7 @@ AC_CHECK_FUNCS([ \
   usleep \
   vasprintf \
   getservbyname \
+  getrandom \
 ])
 AM_CONDITIONAL(STRLCPY_IMPL, [test x"$ac_cv_func_strlcpy" = xno])
 

event-config.h.cmake

@@ -75,11 +75,8 @@
 /* Define to 1 if you have the declaration of `KERN_ARND'. */
 #define EVENT__HAVE_DECL_KERN_ARND @EVENT__HAVE_DECL_KERN_ARND@
 
-/* Define to 1 if you have the declaration of `KERN_RANDOM'. */
-#define EVENT__HAVE_DECL_KERN_RANDOM @EVENT__HAVE_DECL_KERN_RANDOM@
-
-/* Define to 1 if you have the declaration of `RANDOM_UUID'. */
-#define EVENT__HAVE_DECL_RANDOM_UUID @EVENT__HAVE_DECL_RANDOM_UUID@
+/* Define to 1 if you have `getrandom' function. */
+#define EVENT__HAVE_GETRANDOM @EVENT__HAVE_GETRANDOM@
 
 /* Define if /dev/poll is available */
 #cmakedefine EVENT__HAVE_DEVPOLL 1
@@ -370,6 +367,9 @@
 /* Define to 1 if you have the <sys/stat.h> header file. */
 #cmakedefine EVENT__HAVE_SYS_STAT_H 1
 
+/* Define to 1 if you have the <sys/random.h> header file. */
+#cmakedefine EVENT__HAVE_SYS_RANDOM_H 1
+
 /* Define to 1 if you have the <sys/sysctl.h> header file. */
 #cmakedefine EVENT__HAVE_SYS_SYSCTL_H 1