diff options
| author | Jan Kara <jack@suse.cz> | 2017-05-26 17:45:45 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-10-12 11:51:26 +0200 |
| commit | 2d605d9188d64e7d2bd96b4ec5bf91434024a25a (patch) | |
| tree | 4177f7a4f531c22a18fc736226e763d7215da847 /fs | |
| parent | 27db1f020373a0681d483cc2d304e018cbd15723 (diff) | |
ext4: fix data corruption for mmap writes
commit a056bdaae7a181f7dcc876cfab2f94538e508709 upstream.
mpage_submit_page() can race with another process growing i_size and
writing data via mmap to the written-back page. As mpage_submit_page()
samples i_size too early, it may happen that ext4_bio_write_page()
zeroes out too large tail of the page and thus corrupts user data.
Fix the problem by sampling i_size only after the page has been
write-protected in page tables by clear_page_dirty_for_io() call.
Reported-by: Michael Zimmer <michael@swarm64.com>
Fixes: cb20d5188366f04d96d2e07b1240cc92170ade40
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/ext4/inode.c | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 1b29efcab3dc..ec28e8ebb984 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2107,15 +2107,29 @@ static int ext4_writepage(struct page *page, static int mpage_submit_page(struct mpage_da_data *mpd, struct page *page) { int len; - loff_t size = i_size_read(mpd->inode); + loff_t size; int err; BUG_ON(page->index != mpd->first_page); + clear_page_dirty_for_io(page); + /* + * We have to be very careful here! Nothing protects writeback path + * against i_size changes and the page can be writeably mapped into + * page tables. So an application can be growing i_size and writing + * data through mmap while writeback runs. clear_page_dirty_for_io() + * write-protects our page in page tables and the page cannot get + * written to again until we release page lock. So only after + * clear_page_dirty_for_io() we are safe to sample i_size for + * ext4_bio_write_page() to zero-out tail of the written page. We rely + * on the barrier provided by TestClearPageDirty in + * clear_page_dirty_for_io() to make sure i_size is really sampled only + * after page tables are updated. + */ + size = i_size_read(mpd->inode); if (page->index == size >> PAGE_SHIFT) len = size & ~PAGE_MASK; else len = PAGE_SIZE; - clear_page_dirty_for_io(page); err = ext4_bio_write_page(&mpd->io_submit, page, len, mpd->wbc, false); if (!err) mpd->wbc->nr_to_write--; |