udf: Apply uid/gid mount options also to new inodes & chown

Currently newly created files belong to current user despite
uid=<number> / gid=<number> mount options. This is confusing to users
(as owner of the file will change after remount / eviction from cache)
and also inconsistent with e.g. FAT with the same mount option. So apply
uid=<number> and gid=<number> also to newly created inodes and similarly
as FAT disallow to change owner of the file in this case.

Reported-by: Steve Kenton <[e-mail]>
Reviewed-by: Pali Rohár <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>

fs/udf/file.c

···
 static int udf_setattr(struct dentry *dentry, struct iattr *attr)
 {
 	struct inode *inode = d_inode(dentry);
+	struct super_block *sb = inode->i_sb;
 	int error;
 
 	error = setattr_prepare(dentry, attr);
 	if (error)
 		return error;
+
+	if ((attr->ia_valid & ATTR_UID) &&
+	    UDF_QUERY_FLAG(sb, UDF_FLAG_UID_SET) &&
+	    !uid_eq(attr->ia_uid, UDF_SB(sb)->s_uid))
+		return -EPERM;
+	if ((attr->ia_valid & ATTR_GID) &&
+	    UDF_QUERY_FLAG(sb, UDF_FLAG_GID_SET) &&
+	    !gid_eq(attr->ia_gid, UDF_SB(sb)->s_gid))
+		return -EPERM;
 
 	if ((attr->ia_valid & ATTR_SIZE) &&
 	    attr->ia_size != i_size_read(inode)) {

fs/udf/ialloc.c

···
 	}
 
 	inode_init_owner(inode, dir, mode);
+	if (UDF_QUERY_FLAG(sb, UDF_FLAG_UID_SET))
+		inode->i_uid = sbi->s_uid;
+	if (UDF_QUERY_FLAG(sb, UDF_FLAG_GID_SET))
+		inode->i_gid = sbi->s_gid;
 
 	iinfo->i_location.logicalBlockNum = block;
 	iinfo->i_location.partitionReferenceNum =