Re: [patch] UBIFS: use kmalloc_array() in recomp_data_node()

[Artem Bityutskiy <dedekind1@gmail.com>]

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On Thu, 2012-11-22 at 14:14 +0300, Dan Carpenter wrote:
> On Thu, Nov 22, 2012 at 12:31:37PM +0200, Artem Bityutskiy wrote:
> > On Sat, 2012-11-17 at 18:11 +0300, Dan Carpenter wrote:
> > >  	out_len = le32_to_cpu(dn->size);
> > > -	buf = kmalloc(out_len * WORST_COMPR_FACTOR, GFP_NOFS);
> > > +	buf = kmalloc_array(out_len, WORST_COMPR_FACTOR, GFP_NOFS);
> > >  	if (!buf)
> > >  		return -ENOMEM;
> > 
> > I think this makes the code unreadable, because we really allocate a
> > buffer, not an array.
> 
> The problem with the original code is that the multiply looks very
> suspect.  Everyone who reads it has to backtrack to find where
> dn->size is capped.
> 
> I guess in one sense we never allocate an array, we always declare
> it on the stack.  We debated the naming and there really isn't a
> good name.  kmalloc_safe() isn't right either.  But anyway, the
> intent is that eventually someone will right a coccinelle script
> which replaces all these allocations with kmalloc_array().
> 
> When I look at this code more, I still don't see a place where
> dn->size is capped.  So I think we *need* the integer overflow
> check as an integer overflow fix and not just as a cleanup.

It is validated in fs/ubifs/io.c in 'ubifs_check_node()'.

'dn' stands for 'direntry node'. We read it from the media and validate
it immediately after we've read it, including 'dn->len'.

The entire code is written with the following assumption that whatever
is read from the flash media is validated.

-- 
Best Regards,
Artem Bityutskiy

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