This is a note to let you know that I've just added the patch titled btrfs: qgroup: fix data leak caused by race between writeback and truncate to the 5.7-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: btrfs-qgroup-fix-data-leak-caused-by-race-between-writeback-and-truncate.patch and it can be found in the queue-5.7 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From fa91e4aa1716004ea8096d5185ec0451e206aea0 Mon Sep 17 00:00:00 2001 From: Qu Wenruo <wqu@xxxxxxxx> Date: Fri, 17 Jul 2020 15:12:05 +0800 Subject: btrfs: qgroup: fix data leak caused by race between writeback and truncate From: Qu Wenruo <wqu@xxxxxxxx> commit fa91e4aa1716004ea8096d5185ec0451e206aea0 upstream. [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@xxxxxxxxxxxxxxx # 4.14+ Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx> Signed-off-by: David Sterba <dsterba@xxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/btrfs/inode.c | 23 ++++++++++------------- 1 file changed, 10 insertions(+), 13 deletions(-) --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -8509,20 +8509,17 @@ 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_DELALLOC | EXTENT_DELALLOC_NEW | Patches currently in stable-queue which might be from wqu@xxxxxxxx are queue-5.7/btrfs-reloc-clear-dead_reloc_tree-bit-for-orphan-roots-to-prevent-runaway-balance.patch queue-5.7/btrfs-qgroup-fix-data-leak-caused-by-race-between-writeback-and-truncate.patch