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author | Zhang Yi <yi.zhang@huawei.com> | 2021-12-25 17:09:37 +0800 |
---|---|---|
committer | Theodore Ts'o <tytso@mit.edu> | 2022-01-10 13:25:55 -0500 |
commit | 5c48a7df91499e371ef725895b2e2d21a126e227 (patch) | |
tree | ee739c183ffbf29a9e58c1a4f8f1a42cf9398cbd /fs/ext4 | |
parent | 298b5c521746d69c07beb2757292fb5ccc1b0f85 (diff) | |
download | linux-5c48a7df91499e371ef725895b2e2d21a126e227.tar.bz2 |
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 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>
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>
Diffstat (limited to 'fs/ext4')
-rw-r--r-- | fs/ext4/inode.c | 37 |
1 files changed, 10 insertions, 27 deletions
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index bca9951634d9..68070f34f0cf 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -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; } |