zdtm: support ext-uid-map flag for full UID/GID range in user namespaces

Tests that use supplementary group IDs beyond the default mapping range
(e.g. GIDs in the billion scale) fail with EINVAL in user namespace mode
because the GIDs are not mapped. Add support for the 'ext-uid-map' test
flag: when set, ZDTM_UID_MAP and ZDTM_GID_MAP are populated with a
full 32-bit identity mapping (0 0 4294967295), allowing the child user
namespace to access the full UID/GID space.

Signed-off-by: DongSunchao <dongsunchao@gmail.com>

Author: DongSunchao

test/zdtm.py

@@ -511,6 +511,10 @@ def start(self):
         else:
             print("Test is SUID")
 
+        if test_flag(self.__desc, 'ext-uid-map'):
+            env['ZDTM_UID_MAP'] = "0 0 4294967295"
+            env['ZDTM_GID_MAP'] = "0 0 4294967295"
+
         if self.__flavor.ns:
             env['ZDTM_NEWNS'] = "1"
             env['ZDTM_ROOT'] = self.__flavor.root

test/zdtm/lib/ns.c

@@ -492,15 +492,20 @@ void ns_create(int argc, char **argv)
 		char pname[PATH_MAX];
 		int fd;
 
+		char *ext_uid_map = getenv("ZDTM_UID_MAP");
+		char *ext_gid_map = getenv("ZDTM_GID_MAP");
+
 		snprintf(pname, sizeof(pname), "/proc/%d/uid_map", pid);
 		fd = open(pname, O_WRONLY);
 		if (fd < 0) {
 			fprintf(stderr, "open(%s): %m\n", pname);
 			exit(1);
 		}
-		if (write(fd, UID_MAP, sizeof(UID_MAP)) < 0) {
-			fprintf(stderr, "write(" UID_MAP "): %m\n");
-			exit(1);
+
+		if (ext_uid_map) {
+			dprintf(fd, "%s", ext_uid_map);
+		} else {
+			write(fd, UID_MAP, sizeof(UID_MAP) - 1);
 		}
 		close(fd);
 
@@ -510,9 +515,11 @@ void ns_create(int argc, char **argv)
 			fprintf(stderr, "open(%s): %m\n", pname);
 			exit(1);
 		}
-		if (write(fd, GID_MAP, sizeof(GID_MAP)) < 0) {
-			fprintf(stderr, "write(" GID_MAP "): %m\n");
-			exit(1);
+
+		if (ext_gid_map) {
+			dprintf(fd, "%s", ext_gid_map);
+		} else {
+			write(fd, GID_MAP, sizeof(GID_MAP) - 1);
 		}
 		close(fd);
 	}

test/zdtm/static/massive_groups.desc

@@ -1 +1 @@
-{'flavor': 'h', 'flags': 'suid'}
+{'flags': 'suid ext-uid-map'}