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

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Message-ID: <20181123124648.GB2842@twin.jikos.cz>
Date:   Fri, 23 Nov 2018 13:46:49 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Pan Bian <bianpan2016@....com>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        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 Fri, Nov 23, 2018 at 06:10:15PM +0800, 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>

Good catch, thanks.

Reviewed-by: David Sterba <dsterba@...e.com>