Re: [PATCH v2] btrfs: qgroup: don't use extent changeset when not needed

[Boris Burkov]

On Wed, Aug 28, 2024 at 07:14:11PM +0300, Fedor Pchelkin wrote:
> The local extent changeset is passed to clear_record_extent_bits() where
> it may have some additional memory dynamically allocated for ulist. When
> qgroup is disabled, the memory is leaked because in this case the
> changeset is not released upon __btrfs_qgroup_release_data() return.
> 
> Since the recorded contents of the changeset are not used thereafter, just
> don't pass it.
> 
> Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
> 
> Reported-by: syzbot+81670362c283f3dd889c@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/lkml/000000000000aa8c0c060ade165e@xxxxxxxxxx
> Fixes: af0e2aab3b70 ("btrfs: qgroup: flush reservations during quota disable")
> Cc: stable@xxxxxxxxxxxxxxx # 6.10+
> Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>

This version looks even better, to me. Thanks for the catch and fix!

Reviewed-by: Boris Burkov <boris@xxxxxx>

> ---
> v2: rework the fix as Qu Wenruo suggested - just don't pass unneeded
>     changeset. Update the commit title and description accordingly.
> 
>  fs/btrfs/qgroup.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 5d57a285d59b..f6118c5f3c9f 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -4344,10 +4344,9 @@ static int __btrfs_qgroup_release_data(struct btrfs_inode *inode,
>  	int ret;
>  
>  	if (btrfs_qgroup_mode(inode->root->fs_info) == BTRFS_QGROUP_MODE_DISABLED) {
> -		extent_changeset_init(&changeset);
>  		return clear_record_extent_bits(&inode->io_tree, start,
>  						start + len - 1,
> -						EXTENT_QGROUP_RESERVED, &changeset);
> +						EXTENT_QGROUP_RESERVED, NULL);
>  	}
>  
>  	/* In release case, we shouldn't have @reserved */
> -- 
> 2.39.2
>