nfsd4: fix acl buffer overrun

4ac7249e "nfsd: use get_acl and
->set_acl" forgets to set the size in the case get_acl() succeeds, so
_posix_to_nfsv4_one() can then write past the end of its allocation.
Symptoms were slab corruption warnings.

Also, some minor cleanup while we're here.  (Among other things, note
that the first few lines guarantee that pacl is non-NULL.)
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4acl.c

@@ -151,17 +151,15 @@ nfsd4_get_nfs4_acl(struct svc_rqst *rqstp, struct dentry *dentry,
 		pacl = posix_acl_from_mode(inode->i_mode, GFP_KERNEL);
 		if (IS_ERR(pacl))
 			return PTR_ERR(pacl);
+	}
 	/* allocate for worst case: one (deny, allow) pair each: */
 	size += 2 * pacl->a_count;
-	}
 
 	if (S_ISDIR(inode->i_mode)) {
 		flags = NFS4_ACL_DIR;
 		dpacl = get_acl(inode, ACL_TYPE_DEFAULT);
 		if (dpacl)
 			size += 2 * dpacl->a_count;
-	} else {
-		dpacl = NULL;
 	}
 
 	*acl = nfs4_acl_new(size);
@@ -170,7 +168,6 @@ nfsd4_get_nfs4_acl(struct svc_rqst *rqstp, struct dentry *dentry,
 		goto out;
 	}
 
-	if (pacl)
 	_posix_to_nfsv4_one(pacl, *acl, flags & ~NFS4_ACL_TYPE_DEFAULT);
 
 	if (dpacl)