[CFT][PATCH 3/3] userns: Unbreak the unprivileged remount tests

A security fix in caused the way the unprivileged remount tests were
using user namespaces to break.  Tweak the way user namespaces are
being used so the test works again.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <redacted>
---

This is what it takes to fix a broken application, in it's full glory.
This fix works even if new functionality does not exist.

 tools/testing/selftests/mount/unprivileged-remount-test.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/mount/unprivileged-remount-test.c b/tools/testing/selftests/mount/unprivileged-remount-test.c
index 9669d375625a..d47227494137 100644
--- a/tools/testing/selftests/mount/unprivileged-remount-test.c
+++ b/tools/testing/selftests/mount/unprivileged-remount-test.c

@@ -144,13 +144,12 @@ static void create_and_enter_userns(void)
 			strerror(errno));
 	}
 
+	if (access("/proc/self/setgroups", F_OK) == 0) {
+		write_file("/proc/self/setgroups", "0");
+	}
 	write_file("/proc/self/uid_map", "0 %d 1", uid);
 	write_file("/proc/self/gid_map", "0 %d 1", gid);
 
-	if (setgroups(0, NULL) != 0) {
-		die("setgroups failed: %s\n",
-			strerror(errno));
-	}
 	if (setgid(0) != 0) {
 		die ("setgid(0) failed %s\n",
 			strerror(errno));

-- 
1.9.1