[PATCH v2 3/4] urngd: Add support for read()ing entropy

[nwfilardo at gmail.com]

From: Nathaniel Wesley Filardo <nwfilardo at gmail.com>

This allows us to attach a hwrng, for example.

At most one sample will be taken every time we also add entropy via the
jitter mechanism.  We won't try reading if the stream hasn't indicated
its readiness, and we'll go back to waiting if ever the stream produces
0 bytes or an error on read.  If the read was successful, we will
optimistically assume it will be next time, too, avoiding the need to
asynchronously wait for sample availability most of the time.

Signed-off-by: Nathaniel Wesley Filardo <nwfilardo at gmail.com>
---
 urngd.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 76 insertions(+), 4 deletions(-)

diff --git a/urngd.c b/urngd.c
index 31181f0..1168674 100644
--- a/urngd.c
+++ b/urngd.c
@@ -61,6 +61,7 @@ unsigned int debug;
 
 struct urngd {
 	struct uloop_fd rnd_fd;
+	struct uloop_fd file_fd;
 	struct rand_data *ec;
 };
 
@@ -72,6 +73,11 @@ static inline void memset_secure(void *s, int c, size_t n)
 	__asm__ __volatile__("" : : "r" (s) : "memory");
 }
 
+static inline bool entropy_file_available(struct urngd *u)
+{
+	return (u->file_fd.fd >= 0) && !(u->file_fd.registered);
+}
+
 static size_t write_entropy(struct urngd *u, struct rand_pool_info *rpi)
 {
 	int ret;
@@ -88,7 +94,7 @@ static size_t write_entropy(struct urngd *u, struct rand_pool_info *rpi)
 	return ret;
 }
 
-static size_t gather_entropy(struct urngd *u)
+static size_t gather_jitter_entropy(struct urngd *u)
 {
 	ssize_t ent;
 	size_t ret = 0;
@@ -110,12 +116,43 @@ static size_t gather_entropy(struct urngd *u)
 	return ret;
 }
 
+static size_t gather_file_entropy(struct urngd *u) {
+	static const size_t file_bytes = 1024;
+	struct rand_pool_info *rpi = alloca(sizeof(*rpi) + file_bytes);
+	ssize_t ent;
+	size_t ret;
+
+	ent = read(u->file_fd.fd, (char *)&rpi->buf[0], file_bytes);
+	if (ent > 0) {
+		rpi->buf_size = ent;
+		rpi->entropy_count = 8 * ent;
+		ret = write_entropy(u, rpi, "file");
+
+		memset_secure(&rpi->buf, 0, ent);
+	} else {
+		if ((ent < 0) && (errno != EAGAIN) && (errno != EWOULDBLOCK))
+			LOG("read(file) error %s\n", strerror(errno));
+		ret = 0;
+
+		uloop_fd_add(&u->file_fd, ULOOP_READ);
+	}
+
+	return ret;
+}
+
 static void low_entropy_cb(struct uloop_fd *ufd, unsigned int events)
 {
 	struct urngd *u = container_of(ufd, struct urngd, rnd_fd);
 
 	DEBUG(2, DEV_RANDOM " signals low entropy\n");
-	gather_entropy(u);
+	gather_jitter_entropy(u);
+	if (entropy_file_available(u))
+		gather_file_entropy(u);
+}
+
+static void file_ready_cb(struct uloop_fd *ufd, unsigned int events)
+{
+	uloop_fd_delete(ufd);
 }
 
 static void urngd_done(struct urngd *u)
@@ -129,6 +166,11 @@ static void urngd_done(struct urngd *u)
 		close(u->rnd_fd.fd);
 		u->rnd_fd.fd = 0;
 	}
+
+	if (u->file_fd.fd >= 0) {
+		close(u->file_fd.fd);
+		u->file_fd.fd = -1;
+	}
 }
 
 static bool urngd_init(struct urngd *u)
@@ -154,6 +196,18 @@ static bool urngd_init(struct urngd *u)
 
 	uloop_fd_add(&u->rnd_fd, ULOOP_WRITE);
 
+	if (u->file_fd.fd >= 0) {
+		int ret;
+
+		u->file_fd.cb = file_ready_cb;
+		ret = uloop_fd_add(&u->file_fd, ULOOP_READ);
+		if (ret == -1 && errno == EPERM) {
+			LOG("File (-f) does not support polling;"
+				" assuming that's OK.\n");
+			u->file_fd.registered = false;
+		}
+	}
+
 	return true;
 }
 
@@ -164,11 +218,24 @@ static int usage(const char *prog)
 #ifdef URNGD_DEBUG
 		"	-d <level>	Enable debug messages\n"
 #endif
+		"	-f <file>	Source entropy from <file>\n"
 		"	-S		Print messages to stdout\n"
 		"\n", prog);
 	return 1;
 }
 
+static void do_opt_file(struct urngd *u, const char *filename)
+{
+	if (u->file_fd.fd >= 0) {
+		close(u->file_fd.fd);
+	}
+
+	u->file_fd.fd = open(filename, O_RDONLY | O_NONBLOCK);
+	if (u->file_fd.fd < 0) {
+		ERROR("%s open failed: %s\n", filename, strerror(errno));
+	}
+}
+
 int main(int argc, char **argv)
 {
 	int ch;
@@ -182,13 +249,18 @@ int main(int argc, char **argv)
 	}
 #endif
 
-	while ((ch = getopt(argc, argv, "d:S")) != -1) {
+	urngd_service.file_fd.fd = -1;
+
+	while ((ch = getopt(argc, argv, "d:f:S")) != -1) {
 		switch (ch) {
 #ifdef URNGD_DEBUG
 		case 'd':
 			debug = atoi(optarg);
 			break;
 #endif
+		case 'f':
+			do_opt_file(&urngd_service, optarg);
+			break;
 		case 'S':
 			ulog_channels = ULOG_STDIO;
 			break;
@@ -207,7 +279,7 @@ int main(int argc, char **argv)
 
 	LOG("v%s started.\n", URNGD_VERSION);
 
-	gather_entropy(&urngd_service);
+	gather_jitter_entropy(&urngd_service);
 
 	uloop_run();
 	uloop_done();
-- 
2.27.0