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

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Message-ID: <20160812101726.GA18531@pc>
Date:	Fri, 12 Aug 2016 11:17:26 +0100
From:	Salah Triki <salah.triki@...il.com>
To:	Luis de Bethencourt <luisbg@....samsung.com>
Cc:	akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] befs: check allocation_group number before use

On Fri, Aug 12, 2016 at 10:38:58AM +0100, Luis de Bethencourt wrote:
> On 12/08/16 08:26, Salah Triki wrote:
> > On Thu, Aug 11, 2016 at 11:56:16AM +0100, Luis de Bethencourt wrote:
> >> 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
> > 
> > Hi Luis,
> > 
> > allocation group number is set to blockno >> BEFS_SB(sb)->ag_shift by 
> > blockno2iaddr(), so if ag_shift is not valid, an out of bound may occur. 
> > By now, thanx to your question ;), I think it's better to check the validity 
> > of ag_shift when the superblock is loaded.
> > 
> > Nack.
> > 
> > Thanx for the question :)
> > Salah 
> > 
> 
> No problem :)
> 
> I will assume the Nack covers patch 1 to 3. Since they are all related.
> 
> Enjoy the weekend,
> Luis

You too.
Salah