linux-kernel - Re: [PATCH 1/4] befs: check allocation

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Date:	Thu, 11 Aug 2016 11:56:16 +0100
From:	Luis de Bethencourt <luisbg@....samsung.com>
To:	Salah Triki <salah.triki@...il.com>, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] befs: check allocation_group number before use

On 10/08/16 23:12, Salah Triki wrote:
> Check that the allocation group number is not greater or equal to the
> number of allocations group in the file system and return BEF_ERR in the
> case of error.
> 
> Signed-off-by: Salah Triki <salah.triki@...il.com>
> ---
>  fs/befs/befs.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/befs/befs.h b/fs/befs/befs.h
> index 55f3ea2..6daf4c4 100644
> --- a/fs/befs/befs.h
> +++ b/fs/befs/befs.h
> @@ -121,6 +121,11 @@ BEFS_I(const struct inode *inode)
>  static inline befs_blocknr_t
>  iaddr2blockno(struct super_block *sb, const befs_inode_addr *iaddr)
>  {
> +	if (iaddr->allocation_group >= BEFS_SB(sb)->num_ags) {
> +		befs_error(sb, "BEFS: Invalid allocation group %u, max is %u",
> +			   iaddr->allocation_group, BEFS_SB(sb)->num_ags);
> +		return BEFS_ERR;
> +	}
>  	return ((iaddr->allocation_group << BEFS_SB(sb)->ag_shift) +
>  		iaddr->start);
>  }
> 

Hi Salah,

To understand why would we check for this. When can this error happen? I mean,
when can iaddr2blockno() be called with an out of bounds allocation group?

Thanks,
Luis