fix print_ipt: segfault if more then one filter with action -j MARK.

BUG: tc filter show ... produce a segmentation fault if more than one
filter rule with action -j MARK exists.

Reason: In print_ipt(...) xtables will be initialzed with a
pointer to the static struct tcipt_globals at xtables_init_all().
Later on the fields .opts and .options_offset of tcipt_globals are
modified. The call of xtables_free_opts(1) at the end of print(...)
does not restore the original values of tcipt_globals for the
modified fields. It only frees some allocated memory and sets
.opts to NULL. This leads to a segmentation fault when print_ipt()
is called for the next filter rule with action -j MARK.

Fix: Cloneing tcipt_globals on the stack as tmp_tcipt_globals and
use it instead of tcipt_globals, so tcipt_globals will be not
modified.
Signed-off-by: Andreas Greve <andreas.greve@a-greve.de>

tc/m_xt.c

@@ -298,7 +298,10 @@ print_ipt(struct action_util *au,FILE * f, struct rtattr *arg)
 	if (arg == NULL)
 		return -1;
 
-	xtables_init_all(&tcipt_globals, NFPROTO_IPV4);
+	/* copy tcipt_globals because .opts will be modified by iptables */
+	struct xtables_globals tmp_tcipt_globals = tcipt_globals;
+
+	xtables_init_all(&tmp_tcipt_globals, NFPROTO_IPV4);
 	set_lib_dir();
 
 	parse_rtattr_nested(tb, TCA_IPT_MAX, arg);
@@ -333,12 +336,12 @@ print_ipt(struct action_util *au,FILE * f, struct rtattr *arg)
 			}
 
 #if (XTABLES_VERSION_CODE >= 6)
-		opts = xtables_options_xfrm(tcipt_globals.orig_opts,
-					    tcipt_globals.opts,
+		opts = xtables_options_xfrm(tmp_tcipt_globals.orig_opts,
+					    tmp_tcipt_globals.opts,
 					    m->x6_options,
 					    &m->option_offset);
 #else
-		opts = xtables_merge_options(tcipt_globals.opts,
+		opts = xtables_merge_options(tmp_tcipt_globals.opts,
 					     m->extra_opts,
 					     &m->option_offset);
 #endif
@@ -346,7 +349,7 @@ print_ipt(struct action_util *au,FILE * f, struct rtattr *arg)
 		fprintf(stderr, " failed to find aditional options for target %s\n\n", optarg);
 		return -1;
 	} else
-		tcipt_globals.opts = opts;
+		tmp_tcipt_globals.opts = opts;
 		} else {
 			fprintf(stderr, " failed to find target %s\n\n",
 				t->u.user.name);