From bf470202dd9f9f5a29dab007fd2cd6c671aecbed Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Thu, 26 Jan 2023 09:51:55 +0100 Subject: [PATCH] fs: gracefully handle ->get_block not mapping bh in __mpage_writepage When filesystem's ->get_block function does not map the buffer head when called from __mpage_writepage(), __mpage_writepage() will happily go and pass bogus bdev and block number to bio allocation routines which leads to crashes sooner or later. E.g. UDF can do this because it doesn't want to allocate blocks from ->writepages callbacks. It allocates blocks on write or page fault but writeback can still spot dirty buffers without underlying blocks allocated e.g. if blocksize < pagesize, the tail page is dirtied (which means all its buffers are dirtied), and truncate extends the file so that some buffer starts to be within i_size. Link: https://lkml.kernel.org/r/20230126085155.26395-1-jack@suse.cz Signed-off-by: Jan Kara Reviewed-by: Christoph Hellwig Cc: Matthew Wilcox Signed-off-by: Andrew Morton --- fs/mpage.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/mpage.c b/fs/mpage.c index 0f8ae95..ce53179 100644 --- a/fs/mpage.c +++ b/fs/mpage.c @@ -532,6 +532,8 @@ static int __mpage_writepage(struct page *page, struct writeback_control *wbc, map_bh.b_size = 1 << blkbits; if (mpd->get_block(inode, block_in_file, &map_bh, 1)) goto confused; + if (!buffer_mapped(&map_bh)) + goto confused; if (buffer_new(&map_bh)) clean_bdev_bh_alias(&map_bh); if (buffer_boundary(&map_bh)) { -- 2.7.4