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ext4: fix an use-after-free issue about data=journal writeback mode 

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 bdf96838ae ("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: bdf96838ae ("ext4: fix race between truncate and __ext4_journalled_writepage()")
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211225090937.712867-1-yi.zhang@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Zhang Yi 2021-12-25 17:09:37 +08:00 committed by Theodore Ts'o
parent 298b5c5217
commit 5c48a7df91
1 changed files with 10 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
fs/ext4/inode.c
View File

@ -1845,30 +1845,16 @@ int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
return 0;
}
static int bget_one(handle_t *handle, struct inode *inode,
struct buffer_head *bh)
{
get_bh(bh);
return 0;
}
static int bput_one(handle_t *handle, struct inode *inode,
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);
@ -1878,14 +1864,6 @@ 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, inode, page_bufs, 0, len,
NULL, bget_one);
}
/*
* We need to release the page lock before we start the
@ -1906,7 +1884,8 @@ 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;
@ -1916,6 +1895,13 @@ 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, inode, page_bufs, 0, len,
NULL, do_journal_get_write_access);
@ -1936,9 +1922,6 @@ 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, inode, page_bufs, 0, len,
NULL, bput_one);
brelse(inode_bh);
return ret;
}