Merge branch 'arc4seed'

arc4random.c

@@ -1,5 +1,6 @@
 /* Portable arc4random.c based on arc4random.c from OpenBSD.
  * Portable version by Chris Davis, adapted for Libevent by Nick Mathewson
+ * Copyright (c) 2010 Chris Davis, Niels Provos, and Nick Mathewson
  *
  * Note that in Libevent, this file isn't compiled directly.  Instead,
  * it's included from evutil_rand.c
@@ -56,6 +57,7 @@
 #include <unistd.h>
 #include <sys/param.h>
 #include <sys/time.h>
+#include <sys/sysctl.h>
 #endif
 #include <limits.h>
 #include <stdlib.h>
@@ -135,29 +137,20 @@ read_all(int fd, unsigned char *buf, size_t count)
 }
 #endif
 
-/* This is adapted from Tor's crypto_seed_rng() */
-static int
-arc4_seed(void)
-{
-	unsigned char buf[ADD_ENTROPY];
-
-	/* local variables */
 #ifdef WIN32
+#define TRY_SEED_WIN32
+static int
+arc4_seed_win32(void)
+{
+	/* This is adapted from Tor's crypto_seed_rng() */
 	static int provider_set = 0;
 	static HCRYPTPROV provider;
-#else
+	unsigned char buf[ADD_ENTROPY];
-	static const char *filenames[] = {
-		"/dev/srandom", "/dev/urandom", "/dev/random", NULL
-	};
-	int fd, i;
-	size_t n;
-#endif
 
-#ifdef WIN32
 	if (!provider_set) {
 		if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
 		    CRYPT_VERIFYCONTEXT)) {
-			if ((unsigned long)GetLastError() != (unsigned long)NTE_BAD_KEYSET)
+			if (GetLastError() != (DWORD)NTE_BAD_KEYSET)
 				return -1;
 		}
 		provider_set = 1;
@@ -168,7 +161,100 @@ arc4_seed(void)
 	memset(buf, 0, sizeof(buf));
 	arc4_seeded_ok = 1;
 	return 0;
-#else
+}
+#endif
+
+#if defined(_EVENT_HAVE_SYS_SYSCTL_H)
+#if _EVENT_HAVE_DECL_CTL_KERN && _EVENT_HAVE_DECL_KERN_RANDOM && _EVENT_HAVE_DECL_RANDOM_UUID
+#define TRY_SEED_SYSCTL_LINUX
+static int
+arc4_seed_sysctl_linux(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;
+	int i, any_set;
+
+	memset(buf, 0, sizeof(buf));
+
+	for (len = 0; len < sizeof(buf); len += n) {
+		n = sizeof(buf) - len;
+
+		if (0 != sysctl(mib, 3, &buf[len], &n, NULL, 0))
+			return -1;
+	}
+	/* make sure that the buffer actually got set. */
+	for (i=any_set=0; i<sizeof(buf); ++i) {
+		any_set |= buf[i];
+	}
+	if (!any_set)
+		return -1;
+
+	arc4_addrandom(buf, sizeof(buf));
+	memset(buf, 0, sizeof(buf));
+	arc4_seeded_ok = 1;
+	return 0;
+}
+#endif
+
+#if _EVENT_HAVE_DECL_CTL_KERN && _EVENT_HAVE_DECL_KERN_ARND
+#define TRY_SEED_SYSCTL_BSD
+static int
+arc4_seed_sysctl_bsd(void)
+{
+	/* Based on code from William Ahern and from OpenBSD, this function
+	 * tries to use the KERN_ARND syscall 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_ARND };
+	unsigned char buf[ADD_ENTROPY];
+	size_t len, n;
+	int i, any_set;
+
+	memset(buf, 0, sizeof(buf));
+
+	len = sizeof(buf);
+	if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) {
+		for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) {
+			n = sizeof(unsigned);
+			if (n + len > sizeof(buf))
+			    n = len - sizeof(buf);
+			if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1)
+				return -1;
+		}
+	}
+	/* make sure that the buffer actually got set. */
+	for (i=any_set=0; i<sizeof(buf); ++i) {
+		any_set |= buf[i];
+	}
+	if (!any_set)
+		return -1;
+
+	arc4_addrandom(buf, sizeof(buf));
+	memset(buf, 0, sizeof(buf));
+	arc4_seeded_ok = 1;
+	return 0;
+}
+#endif
+#endif /* defined(_EVENT_HAVE_SYS_SYSCTL_H) */
+
+#ifndef WIN32
+#define TRY_SEED_URANDOM
+static int
+arc4_seed_urandom(void)
+{
+	/* This is adapted from Tor's crypto_seed_rng() */
+	static const char *filenames[] = {
+		"/dev/srandom", "/dev/urandom", "/dev/random", NULL
+	};
+	unsigned char buf[ADD_ENTROPY];
+	int fd, i;
+	size_t n;
+
 	for (i = 0; filenames[i]; ++i) {
 		fd = open(filenames[i], O_RDONLY, 0);
 		if (fd<0)
@@ -184,7 +270,33 @@ arc4_seed(void)
 	}
 
 	return -1;
+}
 #endif
+
+static int
+arc4_seed(void)
+{
+	int ok = 0;
+	/* We try every method that might work, and don't give up even if one
+	 * does seem to work.  There's no real harm in over-seeding, and if
+	 * one of these sources turns out to be broken, that would be bad. */
+#ifdef TRY_SEED_WIN32
+	if (0 == arc4_seed_win32())
+		ok = 1;
+#endif
+#ifdef TRY_SEED_SYSCTL_LINUX
+	if (0 == arc4_seed_sysctl_linux())
+		ok = 1;
+#endif
+#ifdef TRY_SEED_SYSCTL_BSD
+	if (0 == arc4_seed_sysctl_bsd())
+		ok = 1;
+#endif
+#ifdef TRY_SEED_URANDOM
+	if (0 == arc4_seed_urandom())
+		ok = 1;
+#endif
+	return ok ? 0 : -1;
 }
 
 static void

configure.in

@@ -46,7 +46,7 @@ AC_ARG_ENABLE(debug-mode,
 AC_PROG_LIBTOOL
 
 dnl   Uncomment "AC_DISABLE_SHARED" to make shared librraries not get
-dnl   built by default.  You can also turn shared libs on and off from 
+dnl   built by default.  You can also turn shared libs on and off from
 dnl   the command line with --enable-shared and --disable-shared.
 dnl AC_DISABLE_SHARED
 AC_SUBST(LIBTOOL_DEPS)
@@ -86,7 +86,7 @@ AC_SUBST(OPENSSL_LIBS)
 
 dnl Checks for header files.
 AC_HEADER_STDC
-AC_CHECK_HEADERS(fcntl.h stdarg.h inttypes.h stdint.h stddef.h poll.h unistd.h sys/epoll.h sys/time.h sys/queue.h sys/event.h sys/param.h sys/ioctl.h sys/select.h sys/devpoll.h port.h netinet/in.h netinet/in6.h sys/socket.h sys/uio.h arpa/inet.h sys/eventfd.h sys/mman.h sys/sendfile.h netdb.h)
+AC_CHECK_HEADERS(fcntl.h stdarg.h inttypes.h stdint.h stddef.h poll.h unistd.h sys/epoll.h sys/time.h sys/queue.h sys/event.h sys/param.h sys/ioctl.h sys/select.h sys/devpoll.h port.h netinet/in.h netinet/in6.h sys/socket.h sys/uio.h arpa/inet.h sys/eventfd.h sys/mman.h sys/sendfile.h netdb.h sys/sysctl.h)
 if test "x$ac_cv_header_sys_queue_h" = "xyes"; then
 	AC_MSG_CHECKING(for TAILQ_FOREACH in sys/queue.h)
 	AC_EGREP_CPP(yes,
@@ -158,6 +158,13 @@ if test "x$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], [], [],
+	   [[#include <sys/types.h>
+	     #include <sys/sysctl.h>]]
+	)
+fi
+
 dnl - check if the macro WIN32 is defined on this compiler.
 dnl - (this is how we check for a windows version of GCC)
 AC_MSG_CHECKING(for WIN32)

evutil_rand.c

@@ -43,6 +43,8 @@
 int
 evutil_secure_rng_init(void)
 {
+	/* call arc4random() now to force it to self-initialize */
+	(void) arc4random();
 	return 0;
 }
 

include/event2/util.h

@@ -532,8 +532,38 @@ const char *evutil_gai_strerror(int err);
  */
 void evutil_secure_rng_get_bytes(void *buf, size_t n);
 
+/**
+ * Seed the secure random number generator if needed, and return 0 on
+ * success or -1 on failure.
+ *
+ * It is okay to call this function more than once; it will still return
+ * 0 if the RNG has been successfully seeded and -1 if it can't be
+ * seeded.
+ *
+ * Ordinarily you don't need to call this function from your own code;
+ * Libevent will seed the RNG itself the first time it needs good random
+ * numbers.  You only need to call it if (a) you want to double-check
+ * that one of the seeding methods did succeed, or (b) you plan to drop
+ * the capability to seed (by chrooting, or dropping capabilities, or
+ * whatever), and you want to make sure that seeding happens before your
+ * program loses the ability to do it.
+ */
 int evutil_secure_rng_init(void);
 
+/** Seed the random number generator with extra random bytes.
+
+    You should almost never need to call this function; it should be
+    sufficient to invoke evutil_secure_rng_init(), or let Libevent take
+    care of calling evutil_secure_rng_init() on its own.
+
+    If you call this function as a _replacement_ for the regular
+    entropy sources, then you need to be sure that your input
+    contains a fairly large amount of strong entropy.  Doing so is
+    notoriously hard: most people who try get it wrong.  Watch out!
+
+    @param dat a buffer full of a strong source of random numbers
+    @param datlen the number of bytes to read from datlen
+ */
 void evutil_secure_rng_add_bytes(const char *dat, size_t datlen);
 
 #ifdef __cplusplus