Re: [PATCH] mm,slub: do not call do_slab_free for kfence object

[Chris Mason]

On 7/29/24 2:19 PM, Rik van Riel wrote:
> In 782f8906f805 the freeing of kfence objects was moved from deep
> inside do_free_slab to the wrapper functions outside. This is a nice
> change, but unfortunately it missed one spot in __kmem_cache_free_bulk.
> 
> This results in a crash like this:
> 
> BUG skbuff_head_cache (Tainted: G S  B       E     ): Padding overwritten. 0xffff88907fea0f00-0xffff88907fea0fff @offset=3840
> 
> slab_err (mm/slub.c:1129)
> free_to_partial_list (mm/slub.c:? mm/slub.c:4036)
> slab_pad_check (mm/slub.c:864 mm/slub.c:1290)
> check_slab (mm/slub.c:?)
> free_to_partial_list (mm/slub.c:3171 mm/slub.c:4036)
> kmem_cache_alloc_bulk (mm/slub.c:? mm/slub.c:4495 mm/slub.c:4586 mm/slub.c:4635)
> napi_build_skb (net/core/skbuff.c:348 net/core/skbuff.c:527 net/core/skbuff.c:549)
> 
> All the other callers to do_free_slab appear to be ok.
> 
> Add a kfence_free check in __kmem_cache_free_bulk to avoid the crash.
> 
> Reported-by: Chris Mason <clm@xxxxxxxx>
> Fixes: 782f8906f805 ("mm/slub: free KFENCE objects in slab_free_hook()")
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>

We found this after bisecting a slab corruption down to the kfence
patch, and with this patch applied we're no longer falling over.  So
thanks Rik!

-chris