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" <ebiederm@xmission.com>

1 files changed, 24 insertions, 8 deletions

diff --git a/tools/testing/selftests/mount/unprivileged-remount-test.c b/tools/testing/selftests/mount/unprivileged-remount-test.c
index 9669d375625a..517785052f1c 100644
--- a/tools/testing/selftests/mount/unprivileged-remount-test.c
+++ b/tools/testing/selftests/mount/unprivileged-remount-test.c
@@ -53,17 +53,14 @@ static void die(char *fmt, ...)
         exit(EXIT_FAILURE);
 }
 
-static void write_file(char *filename, char *fmt, ...)
+static void vmaybe_write_file(bool enoent_ok, char *filename, char *fmt, va_list ap)
 {
         char buf[4096];
         int fd;
         ssize_t written;
         int buf_len;
-        va_list ap;
 
-        va_start(ap, fmt);
         buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
-        va_end(ap);
         if (buf_len < 0) {
                 die("vsnprintf failed: %s\n",
                     strerror(errno));
@@ -74,6 +71,8 @@ static void write_file(char *filename, char *fmt, ...)
 
         fd = open(filename, O_WRONLY);
         if (fd < 0) {
+                if ((errno == ENOENT) && enoent_ok)
+                        return;
                 die("open of %s failed: %s\n",
                     filename, strerror(errno));
         }
@@ -92,6 +91,26 @@ static void write_file(char *filename, char *fmt, ...)
         }
 }
 
+static void maybe_write_file(char *filename, char *fmt, ...)
+{
+        va_list ap;
+
+        va_start(ap, fmt);
+        vmaybe_write_file(true, filename, fmt, ap);
+        va_end(ap);
+
+}
+
+static void write_file(char *filename, char *fmt, ...)
+{
+        va_list ap;
+
+        va_start(ap, fmt);
+        vmaybe_write_file(false, filename, fmt, ap);
+        va_end(ap);
+
+}
+
 static int read_mnt_flags(const char *path)
 {
         int ret;
@@ -144,13 +163,10 @@ static void create_and_enter_userns(void)
                         strerror(errno));
         }
 
+        maybe_write_file("/proc/self/setgroups", "deny");
         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));