udf: Make stat on symlink report symlink length as st_size

UDF encodes symlinks in a more complex fashion and thus i_size of a
symlink does not match the lenght of a string returned by readlink(2).
This confuses some applications (see bug 191241) and may be considered a
violation of POSIX. Fix the problem by reading the link into page cache
in response to stat(2) call and report the length of the decoded path.
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/inode.c

@@ -1547,7 +1547,7 @@ static int udf_read_inode(struct inode *inode, bool hidden_inode)
 		break;
 	case ICBTAG_FILE_TYPE_SYMLINK:
 		inode->i_data.a_ops = &udf_symlink_aops;
-		inode->i_op = &page_symlink_inode_operations;
+		inode->i_op = &udf_symlink_inode_operations;
 		inode_nohighmem(inode);
 		inode->i_mode = S_IFLNK | S_IRWXUGO;
 		break;

fs/udf/namei.c

@@ -931,7 +931,7 @@ static int udf_symlink(struct inode *dir, struct dentry *dentry,
 	}
 
 	inode->i_data.a_ops = &udf_symlink_aops;
-	inode->i_op = &page_symlink_inode_operations;
+	inode->i_op = &udf_symlink_inode_operations;
 	inode_nohighmem(inode);
 
 	if (iinfo->i_alloc_type != ICBTAG_FLAG_AD_IN_ICB) {

fs/udf/symlink.c

@@ -152,9 +152,39 @@ static int udf_symlink_filler(struct file *file, struct page *page)
 	return err;
 }
 
+static int udf_symlink_getattr(struct vfsmount *mnt, struct dentry *dentry,
+			       struct kstat *stat)
+{
+	struct inode *inode = d_backing_inode(dentry);
+	struct page *page;
+
+	generic_fillattr(inode, stat);
+	page = read_mapping_page(inode->i_mapping, 0, NULL);
+	if (IS_ERR(page))
+		return PTR_ERR(page);
+	/*
+	 * UDF uses non-trivial encoding of symlinks so i_size does not match
+	 * number of characters reported by readlink(2) which apparently some
+	 * applications expect. Also POSIX says that "The value returned in the
+	 * st_size field shall be the length of the contents of the symbolic
+	 * link, and shall not count a trailing null if one is present." So
+	 * let's report the length of string returned by readlink(2) for
+	 * st_size.
+	 */
+	stat->size = strlen(page_address(page));
+	put_page(page);
+
+	return 0;
+}
+
 /*
  * symlinks can't do much...
  */
 const struct address_space_operations udf_symlink_aops = {
 	.readpage		= udf_symlink_filler,
 };
+
+const struct inode_operations udf_symlink_inode_operations = {
+	.get_link	= page_get_link,
+	.getattr	= udf_symlink_getattr,
+};

fs/udf/udfdecl.h

@@ -84,6 +84,7 @@ extern const struct inode_operations udf_dir_inode_operations;
 extern const struct file_operations udf_dir_operations;
 extern const struct inode_operations udf_file_inode_operations;
 extern const struct file_operations udf_file_operations;
+extern const struct inode_operations udf_symlink_inode_operations;
 extern const struct address_space_operations udf_aops;
 extern const struct address_space_operations udf_adinicb_aops;
 extern const struct address_space_operations udf_symlink_aops;