Use atomic key generation in all cases

dbutil.c

@@ -681,4 +681,21 @@ time_t monotonic_now() {
 	return time(NULL);
 }
+void fsync_parent_dir(const char* fn) {
+#ifdef HAVE_LIBGEN_H
+	char *fn_dir = m_strdup(fn);
+	char *dir = dirname(fn_dir);
+	int dirfd = open(dir, O_RDONLY);
+
+	if (dirfd != -1) {
+		if (fsync(dirfd) != 0) {
+			TRACE(("fsync of directory %s failed: %s", dir, strerror(errno)))
+		}
+		m_close(dirfd);
+	} else {
+		TRACE(("error opening directory %s for fsync: %s", dir, strerror(errno)))
+	}
+	free(fn_dir);
+#endif
+}

dbutil.h

@@ -89,4 +89,6 @@ time_t monotonic_now(void);
 char * expand_homedir_path(const char *inpath);
+void fsync_parent_dir(const char* fn);
+
 #endif /* DROPBEAR_DBUTIL_H_ */

dropbearkey.c

@@ -241,7 +241,7 @@ int main(int argc, char ** argv) {
 	}
 	fprintf(stderr, "Generating key, this may take a while...\n");
-	if (signkey_generate(keytype, bits, filename) == DROPBEAR_FAILURE)
+	if (signkey_generate(keytype, bits, filename, 0) == DROPBEAR_FAILURE)
 	{
 		dropbear_exit("Failed to generate key.\n");
 	}

gensignkey.c

@@ -76,10 +76,12 @@ static int get_default_bits(enum signkey_type keytype)
 	}
 }
-int signkey_generate(enum signkey_type keytype, int bits, const char* filename)
+/* if skip_exist is set it will silently return if the key file exists */
+int signkey_generate(enum signkey_type keytype, int bits, const char* filename, int skip_exist)
 {
 	sign_key * key = NULL;
 	buffer *buf = NULL;
+	char *fn_temp = NULL;
 	int ret = DROPBEAR_FAILURE;
 	if (bits == 0)
 	{
@@ -126,10 +128,37 @@ int signkey_generate(enum signkey_type keytype, int bits, const char* filename)
 	sign_key_free(key);
 	key = NULL;
 	buf_setpos(buf, 0);
-	ret = buf_writefile(buf, filename);
-	buf_burn(buf);
-	buf_free(buf);
-	buf = NULL;
+	fn_temp = m_malloc(strlen(filename) + 30);
+	snprintf(fn_temp, strlen(filename)+30, "%s.tmp%d", filename, getpid());
+	ret = buf_writefile(buf, fn_temp);
+
+	if (ret == DROPBEAR_FAILURE) {
+		goto out;
+	}
+
+	if (link(fn_temp, filename) < 0) {
+		/* If generating keys on connection (skipexist) it's OK to get EEXIST 
+		- we probably just lost a race with another connection to generate the key */
+		if (!(skip_exist && errno == EEXIST)) {
+			dropbear_log(LOG_ERR, "Failed moving key file to %s: %s", filename,
+				strerror(errno));
+			/* XXX fallback to non-atomic copy for some filesystems? */
+			ret = DROPBEAR_FAILURE;
+			goto out;
+		}
+	}
+
+out:
+	if (buf) {
+		buf_burn(buf);
+		buf_free(buf);
+	}
+	
+	if (fn_temp) {
+		unlink(fn_temp);
+		m_free(fn_temp);
+	}
+
 	return ret;
 }

gensignkey.h

@@ -3,6 +3,6 @@
 #include "signkey.h"
-int signkey_generate(enum signkey_type type, int bits, const char* filename);
+int signkey_generate(enum signkey_type type, int bits, const char* filename, int skip_exist);
 #endif

svr-kex.c

@@ -93,29 +93,9 @@ void recv_msg_kexdh_init() {
 #if DROPBEAR_DELAY_HOSTKEY
-static void fsync_parent_dir(const char* fn) {
-#ifdef HAVE_LIBGEN_H
-	char *fn_dir = m_strdup(fn);
-	char *dir = dirname(fn_dir);
-	int dirfd = open(dir, O_RDONLY);
-
-	if (dirfd != -1) {
-		if (fsync(dirfd) != 0) {
-			TRACE(("fsync of directory %s failed: %s", dir, strerror(errno)))
-		}
-		m_close(dirfd);
-	} else {
-		TRACE(("error opening directory %s for fsync: %s", dir, strerror(errno)))
-	}
-
-	free(fn_dir);
-#endif
-}
-
 static void svr_ensure_hostkey() {
 	const char* fn = NULL;
-	char *fn_temp = NULL;
 	enum signkey_type type = ses.newkeys->algo_hostkey;
 	void **hostkey = signkey_key_ptr(svr_opts.hostkey, type);
 	int ret = DROPBEAR_FAILURE;
@@ -151,28 +131,10 @@ static void svr_ensure_hostkey() {
 		return;
 	}
-	fn_temp = m_malloc(strlen(fn) + 20);
-	snprintf(fn_temp, strlen(fn)+20, "%s.tmp%d", fn, getpid());
-
-	if (signkey_generate(type, 0, fn_temp) == DROPBEAR_FAILURE) {
+	if (signkey_generate(type, 0, fn, 1) == DROPBEAR_FAILURE) {
 		goto out;
 	}
-
-	if (link(fn_temp, fn) < 0) {
-		/* It's OK to get EEXIST - we probably just lost a race
-		with another connection to generate the key */
-		if (errno != EEXIST) {
-			dropbear_log(LOG_ERR, "Failed moving key file to %s: %s", fn,
-				strerror(errno));
-			/* XXX fallback to non-atomic copy for some filesystems? */
-			goto out;
-		}
-	}
-
-	/* ensure directory update is flushed to disk, otherwise we can end up
-	with zero-byte hostkey files if the power goes off */
-	fsync_parent_dir(fn);
-
+	
 	ret = readhostkey(fn, svr_opts.hostkey, &type);
 	if (ret == DROPBEAR_SUCCESS) {
@@ -190,11 +152,6 @@ static void svr_ensure_hostkey() {
 	}
 out:
-	if (fn_temp) {
-		unlink(fn_temp);
-		m_free(fn_temp);
-	}
-
 	if (ret == DROPBEAR_FAILURE)
 	{
 		dropbear_exit("Couldn't read or generate hostkey %s", fn);