linux-kernel - Re: [PATCH] btrfs: relocation: set trans to be NULL after free

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Message-ID: <1202a51d-8e91-2a72-e12f-8bb6090bd714@gmx.com>
Date:   Fri, 23 Nov 2018 19:18:52 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Pan Bian <bianpan2016@....com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Cc:     Wang Shilong <wangsl.fnst@...fujitsu.com>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: relocation: set trans to be NULL after free



On 2018/11/23 下午6:10, Pan Bian wrote:
> The function relocate_block_group calls btrfs_end_transaction to release
> trans when update_backref_cache returns 1, and then continues the loop
> body. If btrfs_block_rsv_refill fails this time, it will jump out the
> loop and the freed trans will be accessed. This may result in a
> use-after-free bug. The patch assigns NULL to trans after trans is
> released so that it will not be accessed.
> 
> Fixes: 0647bf564f1("Btrfs: improve forever loop when doing balance
> relocation")
> 
> Signed-off-by: Pan Bian <bianpan2016@....com>

Reviewed-by: Qu Wenruo <wqu@...e.com>

Thanks,
Qu

> ---
>  fs/btrfs/relocation.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index 924116f..a3f75b8 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -3959,6 +3959,7 @@ static noinline_for_stack int relocate_block_group(struct reloc_control *rc)
>  restart:
>  		if (update_backref_cache(trans, &rc->backref_cache)) {
>  			btrfs_end_transaction(trans);
> +			trans = NULL;
>  			continue;
>  		}
>  
> 



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