fs: don't allocate blocks beyond EOF from __mpage_writepage

When __mpage_writepage() is called for a page beyond EOF, it will go and
allocate all blocks underlying the page.  This is not only unnecessary but
this way blocks can get leaked (e.g.  if a page beyond EOF is marked dirty
but in the end write fails and i_size is not extended).

Link: https://lkml.kernel.org/r/20230103104430.27749-1-jack@suse.czSigned-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/mpage.c

@@ -524,6 +524,12 @@ static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
 	 */
 	BUG_ON(!PageUptodate(page));
 	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
+	/*
+	 * Whole page beyond EOF? Skip allocating blocks to avoid leaking
+	 * space.
+	 */
+	if (block_in_file >= (i_size + (1 << blkbits) - 1) >> blkbits)
+		goto page_is_mapped;
 	last_block = (i_size - 1) >> blkbits;
 	map_bh.b_page = page;
 	for (page_block = 0; page_block < blocks_per_page; ) {