[v2,1/2] btrfs: qgroup: Fix the wrong target io_tree when freeing reserved data space
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Message ID 20190916120239.12570-1-wqu@suse.com
State New
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  • [v2,1/2] btrfs: qgroup: Fix the wrong target io_tree when freeing reserved data space
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Commit Message

Qu Wenruo Sept. 16, 2019, 12:02 p.m. UTC
[BUG]
Under the follow case with qgroup enabled, if some error happened after
we have reserved delalloc space, then in error handling path, we could
cause qgroup data space leakage:

From btrfs_truncate_block() in inode.c:

	ret = btrfs_delalloc_reserve_space(inode, &data_reserved,
					   block_start, blocksize);
	if (ret)
		goto out;

again:
	page = find_or_create_page(mapping, index, mask);
	if (!page) {
		btrfs_delalloc_release_space(inode, data_reserved,
					     block_start, blocksize, true);
		btrfs_delalloc_release_extents(BTRFS_I(inode), blocksize, true);
		ret = -ENOMEM;
		goto out;
	}

[CAUSE]
In above case, btrfs_delalloc_reserve_space() will call
btrfs_qgroup_reserve_data() and mark the io_tree range with
EXTENT_QGROUP_RESERVED flag.

In the error handling path, we have the following call stack:
btrfs_delalloc_release_space()
|- btrfs_free_reserved_data_space()
   |- btrsf_qgroup_free_data()
      |- __btrfs_qgroup_release_data(reserved=@reserved, free=1)
         |- qgroup_free_reserved_data(reserved=@reserved)
            |- clear_record_extent_bits();
            |- freed += changeset.bytes_changed;

However due to a completion bug, qgroup_free_reserved_data() will clear
EXTENT_QGROUP_RESERVED flag in BTRFS_I(inode)->io_failure_tree, other
than the correct BTRFS_I(inode)->io_tree.
Since io_failure_tree is never marked with that flag,
btrfs_qgroup_free_data() will not free any data reserved space at all,
causing a leakage.

This type of error handling can only be triggered by errors outside of
qgroup code. So EDQUOT error from qgroup can't trigger it.

[FIX]
Fix the wrong target io_tree.

Reported-by: Josef Bacik <josef@toxicpanda.com>
Fixes: bc42bda22345 ("btrfs: qgroup: Fix qgroup reserved space underflow by only freeing reserved ranges")
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Changelog:
v2:
- Commit message polishment
  Use proper call chain to describe the error, as it's pretty deep.
  And rephrase how to trigger the bug.
---
 fs/btrfs/qgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Nikolay Borisov Sept. 24, 2019, 9:03 a.m. UTC | #1
On 16.09.19 г. 15:02 ч., Qu Wenruo wrote:
> [BUG]
> Under the follow case with qgroup enabled, if some error happened after
> we have reserved delalloc space, then in error handling path, we could
> cause qgroup data space leakage:
> 
> From btrfs_truncate_block() in inode.c:
> 
> 	ret = btrfs_delalloc_reserve_space(inode, &data_reserved,
> 					   block_start, blocksize);
> 	if (ret)
> 		goto out;
> 
> again:
> 	page = find_or_create_page(mapping, index, mask);
> 	if (!page) {
> 		btrfs_delalloc_release_space(inode, data_reserved,
> 					     block_start, blocksize, true);
> 		btrfs_delalloc_release_extents(BTRFS_I(inode), blocksize, true);
> 		ret = -ENOMEM;
> 		goto out;
> 	}
> 
> [CAUSE]
> In above case, btrfs_delalloc_reserve_space() will call
> btrfs_qgroup_reserve_data() and mark the io_tree range with
> EXTENT_QGROUP_RESERVED flag.
> 
> In the error handling path, we have the following call stack:
> btrfs_delalloc_release_space()
> |- btrfs_free_reserved_data_space()
>    |- btrsf_qgroup_free_data()
>       |- __btrfs_qgroup_release_data(reserved=@reserved, free=1)
>          |- qgroup_free_reserved_data(reserved=@reserved)
>             |- clear_record_extent_bits();
>             |- freed += changeset.bytes_changed;
> 
> However due to a completion bug, qgroup_free_reserved_data() will clear
> EXTENT_QGROUP_RESERVED flag in BTRFS_I(inode)->io_failure_tree, other
> than the correct BTRFS_I(inode)->io_tree.
> Since io_failure_tree is never marked with that flag,
> btrfs_qgroup_free_data() will not free any data reserved space at all,
> causing a leakage.
> 
> This type of error handling can only be triggered by errors outside of
> qgroup code. So EDQUOT error from qgroup can't trigger it.
> 
> [FIX]
> Fix the wrong target io_tree.
> 
> Reported-by: Josef Bacik <josef@toxicpanda.com>
> Fixes: bc42bda22345 ("btrfs: qgroup: Fix qgroup reserved space underflow by only freeing reserved ranges")
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
> Changelog:
> v2:
> - Commit message polishment
>   Use proper call chain to describe the error, as it's pretty deep.
>   And rephrase how to trigger the bug.
> ---
>  fs/btrfs/qgroup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 2891b57b9e1e..64bdc3e3652d 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -3492,7 +3492,7 @@ static int qgroup_free_reserved_data(struct inode *inode,
>  		 * EXTENT_QGROUP_RESERVED, we won't double free.
>  		 * So not need to rush.
>  		 */
> -		ret = clear_record_extent_bits(&BTRFS_I(inode)->io_failure_tree,
> +		ret = clear_record_extent_bits(&BTRFS_I(inode)->io_tree,
>  				free_start, free_start + free_len - 1,
>  				EXTENT_QGROUP_RESERVED, &changeset);
>  		if (ret < 0)
>
David Sterba Sept. 24, 2019, 4:22 p.m. UTC | #2
On Mon, Sep 16, 2019 at 08:02:38PM +0800, Qu Wenruo wrote:
[...]

1 and 2 added to misc-next, thanks.

Patch
diff mbox series

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 2891b57b9e1e..64bdc3e3652d 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -3492,7 +3492,7 @@  static int qgroup_free_reserved_data(struct inode *inode,
 		 * EXTENT_QGROUP_RESERVED, we won't double free.
 		 * So not need to rush.
 		 */
-		ret = clear_record_extent_bits(&BTRFS_I(inode)->io_failure_tree,
+		ret = clear_record_extent_bits(&BTRFS_I(inode)->io_tree,
 				free_start, free_start + free_len - 1,
 				EXTENT_QGROUP_RESERVED, &changeset);
 		if (ret < 0)