linux-kernel - Re: [PATCH] nilfs2: fix potential use after free

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Message-Id: <20181203.181051.1348099310050315226.konishi.ryusuke@lab.ntt.co.jp>
Date:   Mon, 03 Dec 2018 18:10:51 +0900 (JST)
From:   Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>
To:     Pan Bian <bianpan2016@....com>
Cc:     linux-nilfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nilfs2: fix potential use after free

Hi, Pan Bian

Thank you for feeding back this patch.
I reviewed this and am thinking this must be sent to upstream.

Did you see any kernel oops on this bug ?

Regards,
Ryusuke Konishi

On Mon, 26 Nov 2018 11:08:29 +0800, Pan Bian <bianpan2016@....com> wrote:
> brelse(bh) is called to drop the reference count of bh when the call
> to nilfs_dat_translate fails. If the reference count hits 0, bh may be
> freed. However, bh->b_page is unlocked and put after that, which may
> result in a use-after-free bug. This patch moves the release operation
> after unlocking and putting the page.
> 
> Signed-off-by: Pan Bian <bianpan2016@....com>
> ---
>  fs/nilfs2/gcinode.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nilfs2/gcinode.c b/fs/nilfs2/gcinode.c
> index aa3c328..a24bb29 100644
> --- a/fs/nilfs2/gcinode.c
> +++ b/fs/nilfs2/gcinode.c
> @@ -73,10 +73,8 @@ int nilfs_gccache_submit_read_data(struct inode *inode, sector_t blkoff,
>  		struct the_nilfs *nilfs = inode->i_sb->s_fs_info;
>  
>  		err = nilfs_dat_translate(nilfs->ns_dat, vbn, &pbn);
> -		if (unlikely(err)) { /* -EIO, -ENOMEM, -ENOENT */
> -			brelse(bh);
> +		if (unlikely(err)) /* -EIO, -ENOMEM, -ENOENT */
>  			goto failed;
> -		}
>  	}
>  
>  	lock_buffer(bh);
> @@ -102,6 +100,8 @@ int nilfs_gccache_submit_read_data(struct inode *inode, sector_t blkoff,
>   failed:
>  	unlock_page(bh->b_page);
>  	put_page(bh->b_page);
> +	if (unlikely(err))
> +		brelse(bh);
>  	return err;
>  }
>  
> -- 
> 2.7.4
> 
>