Tools: hv: kvp: Fix a warning of buffer overflow with gcc 8.0.1

The patch fixes:

hv_kvp_daemon.c: In function 'kvp_set_ip_info':
hv_kvp_daemon.c:1305:2: note: 'snprintf' output between 41 and 4136 bytes
into a destination of size 4096

The "(unsigned int)str_len" is to avoid:

hv_kvp_daemon.c:1309:30: warning: comparison of integer expressions of
different signedness: 'int' and 'long unsigned int' [-Wsign-compare]

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 13 insertions, 2 deletions

diff --git a/tools/hv/hv_kvp_daemon.c b/tools/hv/hv_kvp_daemon.c
index bbb2a8ef367c..d7e06fe0270e 100644
--- a/tools/hv/hv_kvp_daemon.c
+++ b/tools/hv/hv_kvp_daemon.c
@@ -1178,6 +1178,7 @@ static int kvp_set_ip_info(char *if_name, struct hv_kvp_ipaddr_value *new_val)
         FILE *file;
         char cmd[PATH_MAX];
         char *mac_addr;
+        int str_len;
 
         /*
          * Set the configuration for the specified interface with
@@ -1301,8 +1302,18 @@ static int kvp_set_ip_info(char *if_name, struct hv_kvp_ipaddr_value *new_val)
          * invoke the external script to do its magic.
          */
 
-        snprintf(cmd, sizeof(cmd), KVP_SCRIPTS_PATH "%s %s",
-                 "hv_set_ifconfig", if_file);
+        str_len = snprintf(cmd, sizeof(cmd), KVP_SCRIPTS_PATH "%s %s",
+                           "hv_set_ifconfig", if_file);
+        /*
+         * This is a little overcautious, but it's necessary to suppress some
+         * false warnings from gcc 8.0.1.
+         */
+        if (str_len <= 0 || (unsigned int)str_len >= sizeof(cmd)) {
+                syslog(LOG_ERR, "Cmd '%s' (len=%d) may be too long",
+                       cmd, str_len);
+                return HV_E_FAIL;
+        }
+
         if (system(cmd)) {
                 syslog(LOG_ERR, "Failed to execute cmd '%s'; error: %d %s",
                                 cmd, errno, strerror(errno));