zdtm: set additional groups along with uids and gids

Currently zdtm doesn't set additional groups when running
tests. It sets uids and gids to some non-root values, but
additional groups remain untouched, which allows tests
to inherit groups list, which leads to different
behaviour depending on a way you run tests.
Signed-off-by: Ruslan Kuprieiev <kupruser@gmail.com>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm.sh

@@ -475,10 +475,12 @@ start_test()
 
 	unset ZDTM_UID
 	unset ZDTM_GID
+	unset ZDTM_GROUPS
 
 	if ! echo $TEST_SUID_LIST | grep -q $tname; then
 		export ZDTM_UID=18943
 		export ZDTM_GID=58467
+		export ZDTM_GROUPS="27495 48244"
 		chmod a+w $tdir
 	fi
 

test/zdtm/lib/test.c

@@ -14,6 +14,7 @@
 #include <sys/stat.h>
 #include <string.h>
 #include <sys/prctl.h>
+#include <grp.h>
 
 #include "zdtmtst.h"
 #include "lock.h"
@@ -120,6 +121,24 @@ void test_init(int argc, char **argv)
 		/* "3" -- run the test */
 	}
 
+	val = getenv("ZDTM_GROUPS");
+	if (val) {
+		char *tok = NULL;
+		unsigned int size = 0, groups[NGROUPS_MAX];
+
+		tok = strtok(val, " ");
+		while (tok) {
+			size++;
+			groups[size - 1] = atoi(tok);
+			tok = strtok(NULL, " ");
+		}
+
+		if (setgroups(size, groups)) {
+			fprintf(stderr, "Can't set groups: %m");
+			exit(1);
+		}
+	}
+
 	val = getenv("ZDTM_GID");
 	if (val && (setgid(atoi(val)) == -1)) {
 		fprintf(stderr, "Can't set gid: %m");