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, 2 insertions, 2 deletions

diff --git a/include/local.h b/include/local.h
index 22859d7..9379446 100644
--- a/include/local.h
+++ b/include/local.h
@@ -7,12 +7,12 @@
 
 struct local_conf {
 	int reuseaddr;
-	char path[UNIX_PATH_MAX];
+	char path[UNIX_PATH_MAX + 1];
 };
 
 struct local_server {
 	int fd;
-	char path[UNIX_PATH_MAX];
+	char path[UNIX_PATH_MAX + 1];
 };
 
 /* callback return values */