src: fix strncpy -Wstringop-truncation warnings

-Wstringop-truncation warning was introduced in GCC-8 as truncation
checker for strncpy and strncat.

Systems using gcc version >= 8 would receive the following warnings:

read_config_yy.c: In function ‘yyparse’:
read_config_yy.y:1594:2: warning: ‘strncpy’ specified bound 16 equals destination size [-Wstringop-truncation]
 1594 |  strncpy(policy->name, $2, CTD_HELPER_NAME_LEN);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
read_config_yy.y:1384:2: warning: ‘strncpy’ specified bound 256 equals destination size [-Wstringop-truncation]
 1384 |  strncpy(conf.stats.logfile, $2, FILENAME_MAXLEN);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
read_config_yy.y:692:2: warning: ‘strncpy’ specified bound 108 equals destination size [-Wstringop-truncation]
  692 |  strncpy(conf.local.path, $2, UNIX_PATH_MAX);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
read_config_yy.y:169:2: warning: ‘strncpy’ specified bound 256 equals destination size [-Wstringop-truncation]
  169 |  strncpy(conf.lockfile, $2, FILENAME_MAXLEN);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
read_config_yy.y:119:2: warning: ‘strncpy’ specified bound 256 equals destination size [-Wstringop-truncation]
  119 |  strncpy(conf.logfile, $2, FILENAME_MAXLEN);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

main.c: In function ‘main’:
main.c:168:5: warning: ‘strncpy’ specified bound 4096 equals destination size [-Wstringop-truncation]
  168 |     strncpy(config_file, argv[i], PATH_MAX);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix the issue by checking for string length first. Also using
snprintf instead.

In addition, correct an off-by-one when warning about maximum config
file path length.

Signed-off-by: Jose M. Guisado Gomez <guigom@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/include/conntrackd.h b/include/conntrackd.h
index 81dff22..fe9ec18 100644
--- a/include/conntrackd.h
+++ b/include/conntrackd.h
@@ -85,9 +85,9 @@ union inet_address {
 #define CONFIG(x) conf.x
 
 struct ct_conf {
-	char logfile[FILENAME_MAXLEN];
+	char logfile[FILENAME_MAXLEN + 1];
 	int syslog_facility;
-	char lockfile[FILENAME_MAXLEN];
+	char lockfile[FILENAME_MAXLEN + 1];
 	int hashsize;			/* hashtable size */
 	int channel_num;
 	int channel_default;
@@ -132,7 +132,7 @@ struct ct_conf {
 		int prio;
 	} sched;
 	struct {
-		char logfile[FILENAME_MAXLEN];
+		char logfile[FILENAME_MAXLEN + 1];
 		int syslog_facility;
 		size_t buffer_size;
 	} stats;