coda: Restrict coda messages to the initial user namespace

Remove the slight chance that uids and gids in coda messages will be
interpreted in the wrong user namespace.

- Only allow processes in the initial user namespace to open the coda
  character device to communicate with coda filesystems.
- Explicitly convert the uids in the coda header into the initial user
  namespace.
- In coda_vattr_to_attr make kuids and kgids from the initial user
  namespace uids and gids in struct coda_vattr that just came from
  userspace.
- In coda_iattr_to_vattr convert kuids and kgids into uids and gids
  in the intial user namespace and store them in struct coda_vattr for
  sending to coda userspace programs.

Nothing needs to be changed with mounts as coda does not support
being mounted in anything other than the initial user namespace.

Cc: Jan Harkes <jaharkes@cs.cmu.edu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

fs/coda/upcall.c

@@ -52,7 +52,7 @@ static void *alloc_upcall(int opcode, int size)
         inp->ih.opcode = opcode;
 	inp->ih.pid = task_pid_nr_ns(current, &init_pid_ns);
 	inp->ih.pgid = task_pgrp_nr_ns(current, &init_pid_ns);
-	inp->ih.uid = current_fsuid();
+	inp->ih.uid = from_kuid(&init_user_ns, current_fsuid());
 
 	return (void*)inp;
 }
@@ -157,7 +157,7 @@ int venus_lookup(struct super_block *sb, struct CodaFid *fid,
 }
 
 int venus_close(struct super_block *sb, struct CodaFid *fid, int flags,
-		vuid_t uid)
+		kuid_t uid)
 {
 	union inputArgs *inp;
 	union outputArgs *outp;
@@ -166,7 +166,7 @@ int venus_close(struct super_block *sb, struct CodaFid *fid, int flags,
 	insize = SIZE(release);
 	UPARG(CODA_CLOSE);
 	
-	inp->ih.uid = uid;
+	inp->ih.uid = from_kuid(&init_user_ns, uid);
         inp->coda_close.VFid = *fid;
         inp->coda_close.flags = flags;