Prevent command_to_be_logged from overflowing (#12947)

* prevent command_to_be_logged from overflowing

* dont access with size

2 files changed, 5 insertions, 6 deletions

diff --git a/libnetdata/libnetdata.c b/libnetdata/libnetdata.c
index 69e1d1cf78..5929d976f9 100644
--- a/libnetdata/libnetdata.c
+++ b/libnetdata/libnetdata.c
@@ -1111,14 +1111,13 @@ char *fgets_trim_len(char *buf, size_t buf_size, FILE *fp, size_t *len) {
 }
 
 int vsnprintfz(char *dst, size_t n, const char *fmt, va_list args) {
+    if(unlikely(!n)) return 0;
+
     int size = vsnprintf(dst, n, fmt, args);
+    dst[n - 1] = '\0';
 
-    if (unlikely((size_t) size > n)) {
-        // truncated
-        size = (int)n;
-    }
+    if (unlikely((size_t) size > n)) size = (int)n;
 
-    dst[size] = '\0';
     return size;
 }
 
diff --git a/libnetdata/popen/popen.c b/libnetdata/popen/popen.c
index fa9dd2b6c0..eaeffd32dd 100644
--- a/libnetdata/popen/popen.c
+++ b/libnetdata/popen/popen.c
@@ -400,4 +400,4 @@ int mypclose(FILE *fp, pid_t pid)
 int netdata_spawn_waitpid(pid_t pid)
 {
     return custom_pclose(NULL, pid);
-}
\ No newline at end of file
+}