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

[Vlastimil Babka <vbabka@suse.cz>]

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).

> 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.

> 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.

Thanks.