Re: [PATCH][2/2] fix unchecked returns from kmalloc() (in mm/slab.c)

[Jesper Juhl]

On Tue, 7 Dec 2004, Jens Axboe wrote:

> On Tue, Dec 07 2004, Jesper Juhl wrote:
> > 
> > Problem reported by Katrina Tsipenyuk and the Fortify Software engineering
> > team in thread with subject "PROBLEM: unchecked returns from kmalloc() in
> > linux-2.6.10-rc2".
> > 
> > Unfortunately I'm not very familliar with the code in question, and since 
> > I didn't find a really good way to deal with a failing kmalloc() here I 
> > settled for second best which is to add a BUG_ON() in case kmalloc fails. 
> > This will at least crash in a sane way at the point the problem occoures 
> > rather than getting strange problems at a (possibly) later time. If 
> > someone who's familliar with how this code works has a better solution 
> > then please step forward :) but in the mean time I think this is at least 
> > a slight improvement over the current situation.
> > 
> > Patch has been compile tested and boot tested and didn't blow up 
> > instantly, but please review before applying.
> > 
> > 
> > Signed-off-by: Jesper Juhl <juhl-lkml@xxxxxx>
> > 
> > diff -up linux-2.6.10-rc3-bk2-orig/mm/slab.c linux-2.6.10-rc3-bk2/mm/slab.c
> > --- linux-2.6.10-rc3-bk2-orig/mm/slab.c	2004-12-06 22:24:56.000000000 +0100
> > +++ linux-2.6.10-rc3-bk2/mm/slab.c	2004-12-07 21:27:20.000000000 +0100
> > @@ -804,6 +804,7 @@ void __init kmem_cache_init(void)
> >  		void * ptr;
> >  		
> >  		ptr = kmalloc(sizeof(struct arraycache_init), GFP_KERNEL);
> > +		BUG_ON(ptr == NULL);	/* FIXME: Can a failed kmalloc be handled better? */
> >  		local_irq_disable();
> >  		BUG_ON(ac_data(&cache_cache) != &initarray_cache.cache);
> >  		memcpy(ptr, ac_data(&cache_cache), sizeof(struct arraycache_init));
> 
> This is pointless, as a NULL deref on memcpy will give you the exact
> same info.
> 
Hmm, now why didn't I think of that. Thanks Jens.
I guess I'm not up to the task of fixing this one. I'll try looking 
harder, but I don't think I can do better in this case.

-- 
Jesper Juhl


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