[PATCH AUTOSEL 4.14 127/127] btrfs: qgroup: fix data leak caused by race between writeback and truncate

Sasha Levin
2020-09-18T02:30:04Z

From: Qu Wenruo <wqu@suse.com>

[ Upstream commit fa91e4aa1716004ea8096d5185ec0451e206aea0 ]

[BUG]
When running tests like generic/013 on test device with btrfs quota
enabled, it can normally lead to data leak, detected at unmount time:

BTRFS warning (device dm-3): qgroup 0/5 has unreleased space, type 0 rsv 4096
------------[ cut here ]------------
WARNING: CPU: 11 PID: 16386 at fs/btrfs/disk-io.c:4142 close_ctree+0x1dc/0x323 [btrfs]
RIP: 0010:close_ctree+0x1dc/0x323 [btrfs]
Call Trace:
btrfs_put_super+0x15/0x17 [btrfs]
generic_shutdown_super+0x72/0x110
kill_anon_super+0x18/0x30
btrfs_kill_super+0x17/0x30 [btrfs]
deactivate_locked_super+0x3b/0xa0
deactivate_super+0x40/0x50
cleanup_mnt+0x135/0x190
__cleanup_mnt+0x12/0x20
task_work_run+0x64/0xb0
__prepare_exit_to_usermode+0x1bc/0x1c0
__syscall_return_slowpath+0x47/0x230
do_syscall_64+0x64/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
---[ end trace caf08beafeca2392 ]---
BTRFS error (device dm-3): qgroup reserved space leaked

[CAUSE]
In the offending case, the offending operations are:
2/6: writev f2X[269 1 0 0 0 0] [1006997,67,288] 0
2/7: truncate f2X[269 1 0 0 48 1026293] 18388 0

The following sequence of events could happen after the writev():
CPU1 (writeback) | CPU2 (truncate)
-----------------------------------------------------------------
btrfs_writepages() |
|- extent_write_cache_pages() |
|- Got page for 1003520 |
| 1003520 is Dirty, no writeback |
| So (!clear_page_dirty_for_io()) |
| gets called for it |
|- Now page 1003520 is Clean. |
| | btrfs_setattr()
| | |- btrfs_setsize()
| | |- truncate_setsize()
| | New i_size is 18388
|- __extent_writepage() |
| |- page_offset() > i_size |
|- btrfs_invalidatepage() |
|- Page is clean, so no qgroup |
callback executed

This means, the qgroup reserved data space is not properly released in
btrfs_invalidatepage() as the page is Clean.

[FIX]
Instead of checking the dirty bit of a page, call
btrfs_qgroup_free_data() unconditionally in btrfs_invalidatepage().

As qgroup rsv are completely bound to the QGROUP_RESERVED bit of
io_tree, not bound to page status, thus we won't cause double freeing
anyway.

Fixes: 0b34c261e235 ("btrfs: qgroup: Prevent qgroup->reserved from going subzero")
CC: stable@vger.kernel.org # 4.14+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/inode.c | 23 ++++++++++-------------
1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 17856e92b93d1..c9e7b92d0f212 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9204,20 +9204,17 @@ again:
/*
* Qgroup reserved space handler
* Page here will be either
- * 1) Already written to disk
- * In this case, its reserved space is released from data rsv map
- * and will be freed by delayed_ref handler finally.
- * So even we call qgroup_free_data(), it won't decrease reserved
- * space.
- * 2) Not written to disk
- * This means the reserved space should be freed here. However,
- * if a truncate invalidates the page (by clearing PageDirty)
- * and the page is accounted for while allocating extent
- * in btrfs_check_data_free_space() we let delayed_ref to
- * free the entire extent.
+ * 1) Already written to disk or ordered extent already submitted
+ * Then its QGROUP_RESERVED bit in io_tree is already cleaned.
+ * Qgroup will be handled by its qgroup_record then.
+ * btrfs_qgroup_free_data() call will do nothing here.
+ *
+ * 2) Not written to disk yet
+ * Then btrfs_qgroup_free_data() call will clear the QGROUP_RESERVED
+ * bit of its io_tree, and free the qgroup reserved data space.
+ * Since the IO will never happen for this page.
*/
- if (PageDirty(page))
- btrfs_qgroup_free_data(inode, NULL, page_start, PAGE_SIZE);
+ btrfs_qgroup_free_data(inode, NULL, page_start, PAGE_SIZE);
if (!inode_evicting) {
clear_extent_bit(tree, page_start, page_end,
EXTENT_LOCKED | EXTENT_DIRTY |
--
2.25.1