fix buffer string bounds issues reported by coverity

Signed-off-by: Peng Tao <bergwolf@gmail.com>

Author: bergwolf

src/exec.c

@@ -197,7 +197,7 @@ static int hyper_setup_exec_user(struct hyper_exec *exec)
 
 	uid_t uid = 0;
 	gid_t gid = 0;
-	int ngroups;
+	int ngroups = 0;
 	gid_t *reallocgroups, *groups = NULL;
 
 	// check the config

src/init.c

@@ -550,12 +550,15 @@ static void hyper_print_uptime(void)
 {
 	char buf[128];
 	int fd = open("/proc/uptime", O_RDONLY);
+	int n;
 
 	if (fd < 0)
 		return;
-	memset(buf, 0, sizeof(buf));
-	if (read(fd, buf, sizeof(buf)))
+	n = read(fd, buf, sizeof(buf)-1);
+	if (n > 0) {
+		buf[n] = 0;
 		fprintf(stdout, "uptime %s\n", buf);
+	}
 
 	close(fd);
 }

src/net.c

@@ -683,7 +683,7 @@ int hyper_setup_hostname(struct hyper_pod *pod)
 int hyper_write_dns_file(int fd, char *field, char **data, int num)
 {
 	int i = 0, len = 0, ret = -1, size;
-	char *buf = NULL;
+	char *newbuf, *buf = NULL;
 
 	if (num == 0)
 		return 0;
@@ -699,11 +699,12 @@ int hyper_write_dns_file(int fd, char *field, char **data, int num)
 	for (i = 0; i < num; i++) {
 		// 1 for space
 		int new_size = size + strlen(data[i]) + 1;
-		buf = realloc(buf, new_size);
-		if (buf == NULL) {
+		newbuf = realloc(buf, new_size + 1);
+		if (newbuf == NULL) {
 			fprintf(stderr, "fail to realloc buff for %s\n", field);
 			goto out;
 		}
+		buf = newbuf;
 		buf[size]= ' ';
 		memcpy(buf + size + 1, data[i], strlen(data[i]));
 		fprintf(stdout, "%s: data: %s\n", field, buf);