[PATCH] gensignkey: ensure host keys are flushed to disk

[Peter Korsgaard]

From: Peter Korsgaard <peter at korsgaard.com>

Otherwise we can end up with an empty host key, breaking logins.

E.G.:

Run dropbear -R and pull power before the host key is writting to disk.
After reboot we have:

ls -l /etc/dropbear/
-rw-------    1 root     root        0 Oct 28 10:41 dropbear_ecdsa_host_key

Which dropbear will try to read and fail:

[599] Oct 28 10:43:43 Early exit: Bad buf_getptr

Signed-off-by: Peter Korsgaard <peter at korsgaard.com>
---
 gensignkey.c |  1 +
 svr-kex.c    | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/gensignkey.c b/gensignkey.c
index 338bbef..06fdfd3 100644
--- a/gensignkey.c
+++ b/gensignkey.c
@@ -41,6 +41,7 @@ static int buf_writefile(buffer * buf, const char * filename) {
 
 out:
 	if (fd >= 0) {
+		fsync(fd);
 		m_close(fd);
 	}
 	return ret;
diff --git a/svr-kex.c b/svr-kex.c
index 337c377..8e76489 100644
--- a/svr-kex.c
+++ b/svr-kex.c
@@ -89,6 +89,7 @@ static void svr_ensure_hostkey() {
 
 	const char* fn = NULL;
 	char *fn_temp = NULL;
+	char *fn_dir = NULL;
 	enum signkey_type type = ses.newkeys->algo_hostkey;
 	void **hostkey = signkey_key_ptr(svr_opts.hostkey, type);
 	int ret = DROPBEAR_FAILURE;
@@ -142,6 +143,22 @@ static void svr_ensure_hostkey() {
 		}
 	}
 
+#ifdef HAVE_LIBGEN_H
+	/* ensure directory update is flushed to disk */
+	fn_dir = strdup(fn);
+	if (fn_dir != NULL) {
+		char *dir = dirname(fn_dir);
+		int dirfd = open(dir, O_RDONLY);
+
+		if (dirfd != -1) {
+			fsync(dirfd);
+			close(dirfd);
+		}
+
+		free(fn_dir);
+	}
+#endif
+
 	ret = readhostkey(fn, svr_opts.hostkey, &type);
 
 	if (ret == DROPBEAR_SUCCESS) {
-- 
2.1.0