userns: Convert ipc to use kuid and kgid where appropriate

- Store the ipc owner and creator with a kuid
- Store the ipc group and the crators group with a kgid.
- Add error handling to ipc_update_perms, allowing it to
  fail if the uids and gids can not be converted to kuids
  or kgids.
- Modify the proc files to display the ipc creator and
  owner in the user namespace of the opener of the proc file.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

ipc/shm.c

@@ -758,7 +758,9 @@ static int shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
 		do_shm_rmid(ns, ipcp);
 		goto out_up;
 	case IPC_SET:
-		ipc_update_perm(&shmid64.shm_perm, ipcp);
+		err = ipc_update_perm(&shmid64.shm_perm, ipcp);
+		if (err)
+			goto out_unlock;
 		shp->shm_ctim = get_seconds();
 		break;
 	default:
@@ -893,10 +895,10 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
 		audit_ipc_obj(&(shp->shm_perm));
 
 		if (!ns_capable(ns->user_ns, CAP_IPC_LOCK)) {
-			uid_t euid = current_euid();
+			kuid_t euid = current_euid();
 			err = -EPERM;
-			if (euid != shp->shm_perm.uid &&
-			    euid != shp->shm_perm.cuid)
+			if (!uid_eq(euid, shp->shm_perm.uid) &&
+			    !uid_eq(euid, shp->shm_perm.cuid))
 				goto out_unlock;
 			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK))
 				goto out_unlock;
@@ -1220,6 +1222,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
 #ifdef CONFIG_PROC_FS
 static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
 {
+	struct user_namespace *user_ns = seq_user_ns(s);
 	struct shmid_kernel *shp = it;
 	unsigned long rss = 0, swp = 0;
 
@@ -1242,10 +1245,10 @@ static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
 			  shp->shm_cprid,
 			  shp->shm_lprid,
 			  shp->shm_nattch,
-			  shp->shm_perm.uid,
-			  shp->shm_perm.gid,
-			  shp->shm_perm.cuid,
-			  shp->shm_perm.cgid,
+			  from_kuid_munged(user_ns, shp->shm_perm.uid),
+			  from_kgid_munged(user_ns, shp->shm_perm.gid),
+			  from_kuid_munged(user_ns, shp->shm_perm.cuid),
+			  from_kgid_munged(user_ns, shp->shm_perm.cgid),
 			  shp->shm_atim,
 			  shp->shm_dtim,
 			  shp->shm_ctim,