From: Zhang Yi yi.zhang@huawei.com

hulk inclusion category: bugfix bugzilla: 185944, https://gitee.com/openeuler/kernel/issues/I4OP92 CVE: NA ---------------------------

Our syzkaller report an use-after-free issue that accessing the freed buffer_head on the writeback page in __ext4_journalled_writepage(). The problem is that if there was a truncate racing with the data=journalled writeback procedure, the writeback length could become zero and bget_one() refuse to get buffer_head's refcount, then the truncate procedure release buffer once we drop page lock, finally, the last ext4_walk_page_buffers() trigger the use-after-free problem.

sync truncate ext4_sync_file() file_write_and_wait_range() ext4_setattr(0) inode->i_size = 0 ext4_writepage() len = 0 __ext4_journalled_writepage() page_bufs = page_buffers(page) ext4_walk_page_buffers(bget_one) <- does not get refcount do_invalidatepage() free_buffer_head() ext4_walk_page_buffers(page_bufs) <- trigger use-after-free

After commit bdf96838aea6 ("ext4: fix race between truncate and __ext4_journalled_writepage()"), we have already handled the racing case, so the bget_one() and bput_one() are not needed. So this patch simply remove these hunk, and recheck the i_size to make it safe.

Fixes: bdf96838aea6 ("ext4: fix race between truncate and __ext4_journalled_writepage()") Signed-off-by: Zhang Yi yi.zhang@huawei.com Reviewed-by: yangerkun yangerkun@huawei.com Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- fs/ext4/inode.c | 35 ++++++++++------------------------- 1 file changed, 10 insertions(+), 25 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 6213816056cd6..e106a9317b429 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -1962,28 +1962,16 @@ int ext4_da_get_block_prep(struct inode *inode, sector_t iblock, return 0; }

-static int bget_one(handle_t *handle, struct buffer_head *bh) -{ - get_bh(bh); - return 0; -} - -static int bput_one(handle_t *handle, struct buffer_head *bh) -{ - put_bh(bh); - return 0; -} - static int __ext4_journalled_writepage(struct page *page, unsigned int len) { struct address_space *mapping = page->mapping; struct inode *inode = mapping->host; - struct buffer_head *page_bufs = NULL; handle_t *handle = NULL; int ret = 0, err = 0; int inline_data = ext4_has_inline_data(inode); struct buffer_head *inode_bh = NULL; + loff_t size;

ClearPageChecked(page);

@@ -1993,14 +1981,6 @@ static int __ext4_journalled_writepage(struct page *page, inode_bh = ext4_journalled_write_inline_data(inode, len, page); if (inode_bh == NULL) goto out; - } else { - page_bufs = page_buffers(page); - if (!page_bufs) { - BUG(); - goto out; - } - ext4_walk_page_buffers(handle, page_bufs, 0, len, - NULL, bget_one); } /* * We need to release the page lock before we start the @@ -2021,7 +2001,8 @@ static int __ext4_journalled_writepage(struct page *page,

lock_page(page); put_page(page); - if (page->mapping != mapping) { + size = i_size_read(inode); + if (page->mapping != mapping || page_offset(page) > size) { /* The page got truncated from under us */ ext4_journal_stop(handle); ret = 0; @@ -2031,6 +2012,13 @@ static int __ext4_journalled_writepage(struct page *page, if (inline_data) { ret = ext4_mark_inode_dirty(handle, inode); } else { + struct buffer_head *page_bufs = page_buffers(page); + + if (page->index == size >> PAGE_SHIFT) + len = size & ~PAGE_MASK; + else + len = PAGE_SIZE; + ret = ext4_walk_page_buffers(handle, page_bufs, 0, len, NULL, do_journal_get_write_access);

@@ -2048,9 +2036,6 @@ static int __ext4_journalled_writepage(struct page *page, out: unlock_page(page); out_no_pagelock: - if (!inline_data && page_bufs) - ext4_walk_page_buffers(NULL, page_bufs, 0, len, - NULL, bput_one); brelse(inode_bh); return ret; }