userns: use union in {g,u}idmap struct

- Add a struct containing two pointer to extents and wrap both the static extent
  array and the struct into a union. This is done in preparation for bumping the
  {g,u}idmap limits for user namespaces.
- Add brackets around anonymous union when using designated initializers to
  initialize members in order to please gcc <= 4.4.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

2 files changed, 31 insertions, 17 deletions

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index c18e01252346..7c83d7f6289b 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -12,13 +12,21 @@
 
 #define UID_GID_MAP_MAX_EXTENTS 5
 
+struct uid_gid_extent {
+        u32 first;
+        u32 lower_first;
+        u32 count;
+};
+
 struct uid_gid_map {    /* 64 bytes -- 1 cache line */
         u32 nr_extents;
-        struct uid_gid_extent {
-                u32 first;
-                u32 lower_first;
-                u32 count;
-        } extent[UID_GID_MAP_MAX_EXTENTS];
+        union {
+                struct uid_gid_extent extent[UID_GID_MAP_MAX_EXTENTS];
+                struct {
+                        struct uid_gid_extent *forward;
+                        struct uid_gid_extent *reverse;
+                };
+        };
 };
 
 #define USERNS_SETGROUPS_ALLOWED 1UL
diff --git a/kernel/user.c b/kernel/user.c
index 00281add65b2..9a20acce460d 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -26,26 +26,32 @@
 struct user_namespace init_user_ns = {
         .uid_map = {
                 .nr_extents = 1,
-                .extent[0] = {
-                        .first = 0,
-                        .lower_first = 0,
-                        .count = 4294967295U,
+                {
+                        .extent[0] = {
+                                .first = 0,
+                                .lower_first = 0,
+                                .count = 4294967295U,
+                        },
                 },
         },
         .gid_map = {
                 .nr_extents = 1,
-                .extent[0] = {
-                        .first = 0,
-                        .lower_first = 0,
-                        .count = 4294967295U,
+                {
+                        .extent[0] = {
+                                .first = 0,
+                                .lower_first = 0,
+                                .count = 4294967295U,
+                        },
                 },
         },
         .projid_map = {
                 .nr_extents = 1,
-                .extent[0] = {
-                        .first = 0,
-                        .lower_first = 0,
-                        .count = 4294967295U,
+                {
+                        .extent[0] = {
+                                .first = 0,
+                                .lower_first = 0,
+                                .count = 4294967295U,
+                        },
                 },
         },
         .count = ATOMIC_INIT(3),