slstatus

commit c83b388a3f8f7a8c8d5a5cfddb6ab397005371a1
parent b759662983a159da8a3c361f4f222287b2e43331
Author: Laslo Hunhold <dev@frign.de>
Date:   Thu, 17 May 2018 23:23:28 +0200

Properly handle *snprintf() errors

Posix guarantees that the resulting string is null-terminated, even if
we have an overflow. Instead of doing what has already been done,
properly warn when there has been an error or overflow, so the user can
do something about it.

Diffstat:
M
slstatus.c
 | 
17
+++++++++++------
M
util.c
 | 
12
++++++------

2 files changed, 17 insertions(+), 12 deletions(-)
diff --git a/slstatus.c b/slstatus.c
@@ -1,4 +1,5 @@
 /* See LICENSE file for copyright and license details. */
+#include <errno.h>
 #include <locale.h>
 #include <signal.h>
 #include <stdio.h>
@@ -53,7 +54,7 @@ main(int argc, char *argv[])
 	struct sigaction act;
 	struct timespec start, current, diff, intspec, wait;
 	size_t i, len;
-	int sflag;
+	int sflag, ret;
 	char status[MAXLEN];
 
 	sflag = 0;
@@ -88,12 +89,16 @@ main(int argc, char *argv[])
 		for (i = len = 0; i < LEN(args); i++) {
 			const char * res = args[i].func(args[i].args);
 			res = (res == NULL) ? unknown_str : res;
-			len += snprintf(status + len, sizeof(status) - len,
-			                args[i].fmt, res);
-
-			if (len >= sizeof(status)) {
-				status[sizeof(status) - 1] = '\0';
+			if ((ret = snprintf(status + len, sizeof(status) - len,
+			                    args[i].fmt, res)) < 0) {
+				fprintf(stderr, "snprintf: %s\n",
+				        strerror(errno));
+				break;
+			} else if ((size_t)ret >= sizeof(status) - len) {
+				fprintf(stderr, "snprintf: Output truncated\n");
+				break;
 			}
+			len += ret;
 		}
 
 		if (sflag) {
diff --git a/util.c b/util.c
@@ -10,15 +10,15 @@ const char *
 bprintf(const char *fmt, ...)
 {
 	va_list ap;
-	size_t len;
+	int ret;
 
 	va_start(ap, fmt);
-	len = vsnprintf(buf, sizeof(buf) - 1, fmt, ap);
-	va_end(ap);
-
-	if (len >= sizeof(buf)) {
-		buf[sizeof(buf)-1] = '\0';
+	if ((ret = vsnprintf(buf, sizeof(buf), fmt, ap)) < 0) {
+		fprintf(stderr, "vsnprintf: %s\n", strerror(errno));
+	} else if ((size_t)ret >= sizeof(buf)) {
+		fprintf(stderr, "vsnprintf: Output truncated\n");
 	}
+	va_end(ap);
 
 	return buf;
 }