[v2,2/2] btrfs: qgroup: Fix reserved data space leak if we have multiple reserve calls
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Message ID 20190916120239.12570-2-wqu@suse.com
State New
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Series
  • [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]
The following script can cause btrfs qgroup data space leak:

  mkfs.btrfs -f $dev
  mount $dev -o nospace_cache $mnt

  btrfs subv create $mnt/subv
  btrfs quota en $mnt
  btrfs quota rescan -w $mnt
  btrfs qgroup limit 128m $mnt/subv

  for (( i = 0; i < 3; i++)); do
          # Create 3 64M holes for latter fallocate to fail
          truncate -s 192m $mnt/subv/file
          xfs_io -c "pwrite 64m 4k" $mnt/subv/file > /dev/null
          xfs_io -c "pwrite 128m 4k" $mnt/subv/file > /dev/null
          sync

          # it's supposed to fail, and each failure will leak at least 64M
          # data space
          xfs_io -f -c "falloc 0 192m" $mnt/subv/file &> /dev/null
          rm $mnt/subv/file
          sync
  done

  # Shouldn't fail after we removed the file
  xfs_io -f -c "falloc 0 64m" $mnt/subv/file

[CAUSE]
Btrfs qgroup data reserve code allow multiple reservations to happen on
a single extent_changeset:
E.g:
	btrfs_qgroup_reserve_data(inode, &data_reserved, 0, SZ_1M);
	btrfs_qgroup_reserve_data(inode, &data_reserved, SZ_1M, SZ_2M);
	btrfs_qgroup_reserve_data(inode, &data_reserved, 0, SZ_4M);

Btrfs qgroup code has its internal tracking to make sure we don't
double-reserve in above example.

The only pattern utlizing this feature is in the main while loop of
btrfs_fallocate() function.

However btrfs_qgroup_reserve_data()'s error handling has a bug in that
on error it clears all ranges in the io_tree with EXTENT_QGROUP_RESERVED
flag but doesn't free previously reserved bytes.

This bug has a two fold effect:
- Clearing EXTENT_QGROUP_RESERVED ranges
  This is the correct behavior, but it prevents
  btrfs_qgroup_check_reserved_leak() to catch the leakage as the
  detector is purely EXTENT_QGROUP_RESERVED flag based.

- Leak the previously reserved data bytes.

The bug manifests when N calls to btrfs_qgroup_reserve_data are made and
the last one fails, leaking space reserved in the previous ones.

[FIX]
Also free previously reserved data bytes when btrfs_qgroup_reserve_data
fails.

Fixes: 524725537023 ("btrfs: qgroup: Introduce btrfs_qgroup_reserve_data function")
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Changelog:
v2:
- Commit message polishment
  Rephrase the multiple btrfs_qgroup_reserve_data() calls ability.
  Rephrase the effect of the bug.
---
 fs/btrfs/qgroup.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Nikolay Borisov Sept. 24, 2019, 9:12 a.m. UTC | #1
On 16.09.19 г. 15:02 ч., Qu Wenruo wrote:
> [BUG]
> The following script can cause btrfs qgroup data space leak:
> 
>   mkfs.btrfs -f $dev
>   mount $dev -o nospace_cache $mnt
> 
>   btrfs subv create $mnt/subv
>   btrfs quota en $mnt
>   btrfs quota rescan -w $mnt
>   btrfs qgroup limit 128m $mnt/subv
> 
>   for (( i = 0; i < 3; i++)); do
>           # Create 3 64M holes for latter fallocate to fail
>           truncate -s 192m $mnt/subv/file
>           xfs_io -c "pwrite 64m 4k" $mnt/subv/file > /dev/null
>           xfs_io -c "pwrite 128m 4k" $mnt/subv/file > /dev/null
>           sync
> 
>           # it's supposed to fail, and each failure will leak at least 64M
>           # data space
>           xfs_io -f -c "falloc 0 192m" $mnt/subv/file &> /dev/null
>           rm $mnt/subv/file
>           sync
>   done
> 
>   # Shouldn't fail after we removed the file
>   xfs_io -f -c "falloc 0 64m" $mnt/subv/file

Was this sent as a separate fstest case?

<snip>
Qu Wenruo Sept. 24, 2019, 9:15 a.m. UTC | #2
On 2019/9/24 下午5:12, Nikolay Borisov wrote:
>
>
> On 16.09.19 г. 15:02 ч., Qu Wenruo wrote:
>> [BUG]
>> The following script can cause btrfs qgroup data space leak:
>>
>>   mkfs.btrfs -f $dev
>>   mount $dev -o nospace_cache $mnt
>>
>>   btrfs subv create $mnt/subv
>>   btrfs quota en $mnt
>>   btrfs quota rescan -w $mnt
>>   btrfs qgroup limit 128m $mnt/subv
>>
>>   for (( i = 0; i < 3; i++)); do
>>           # Create 3 64M holes for latter fallocate to fail
>>           truncate -s 192m $mnt/subv/file
>>           xfs_io -c "pwrite 64m 4k" $mnt/subv/file > /dev/null
>>           xfs_io -c "pwrite 128m 4k" $mnt/subv/file > /dev/null
>>           sync
>>
>>           # it's supposed to fail, and each failure will leak at least 64M
>>           # data space
>>           xfs_io -f -c "falloc 0 192m" $mnt/subv/file &> /dev/null
>>           rm $mnt/subv/file
>>           sync
>>   done
>>
>>   # Shouldn't fail after we removed the file
>>   xfs_io -f -c "falloc 0 64m" $mnt/subv/file
>
> Was this sent as a separate fstest case?

Yep.

https://patchwork.kernel.org/patch/11145871/

Thanks,
Qu

>
> <snip>
>

Patch
diff mbox series

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 64bdc3e3652d..59f6a9981087 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -3448,6 +3448,9 @@  int btrfs_qgroup_reserve_data(struct inode *inode,
 	while ((unode = ulist_next(&reserved->range_changed, &uiter)))
 		clear_extent_bit(&BTRFS_I(inode)->io_tree, unode->val,
 				 unode->aux, EXTENT_QGROUP_RESERVED, 0, 0, NULL);
+	/* Also free data bytes of already reserved one */
+	btrfs_qgroup_free_refroot(root->fs_info, root->root_key.objectid,
+				  orig_reserved, BTRFS_QGROUP_RSV_DATA);
 	extent_changeset_release(reserved);
 	return ret;
 }