Re: [PATCH 3/5] mm/slub: Improve redzone check and zeroing for krealloc()

[Feng Tang]

On Tue, Sep 10, 2024 at 03:15:36PM +0200, Vlastimil Babka wrote:
> On 9/9/24 03:29, Feng Tang wrote:
> > For current krealloc(), one problem is its caller doesn't know what's
> > the actual request size, say the object is 64 bytes kmalloc one, but
> 
> It's more accurate to say the caller doesn't pass the old size (it might
> actually know it).

Right!

> 
> > the original caller may only requested 48 bytes. And when krealloc()
> > shrinks or grows in the same object, or allocate a new bigger object,
> > it lacks this 'original size' information to do accurate data preserving
> > or zeroing (when __GFP_ZERO is set).
> 
> Let's describe the problem specifically by adding:
> 
> Thus with slub debug redzone and object tracking enabled, parts of the
> object after krealloc() might contain redzone data instead of zeroes, which
> is violating the __GFP_ZERO guarantees.
 
Will add it. Thanks for the enhancement!

> > And when some slub debug option is enabled, kmalloc caches do have this
> > 'orig_size' feature. So utilize it to do more accurate data handling,
> > as well as enforce the kmalloc-redzone sanity check.
> > 
> > The krealloc() related code is moved from slab_common.c to slub.c for
> > more efficient function calling.
> 
> Agreed with Danilo that having the move as separate preparatory patch would
> make review easier.

Yes and will do.

Thanks,
Feng

> Thanks.
>