Re: [PATCH] keys: prevent slab cache merging for key_jar

[Jarkko Sakkinen <jarkko@kernel.org>]

On Fri, Jun 05, 2026 at 02:16:00PM +0200, Vlastimil Babka (SUSE) wrote:
> On 6/4/26 14:50, Mohammed EL Kadiri wrote:
> > The key_jar slab cache holds struct key objects containing cryptographic
> > keys, authentication tokens, and keyring linkage. This cache currently
> > lacks merge prevention, allowing the SLUB allocator to merge it with
> > other similarly-sized caches.
> > 
> > On a default Ubuntu 6.17.0-23-generic system, key_jar has 5 aliases,
> > meaning 5 unrelated object types share its slab pages. struct key is
> > 224 bytes, placed in 256-byte slabs alongside biovec-16, maple_node,
> > ip6_dst_cache, task_delay_info, and kmalloc-256 users.
> > 
> > Cross-cache heap exploitation is a well-documented attack class
> > (CVE-2022-29582, CVE-2022-2588, CVE-2021-22555) where slab cache
> > merging enables type confusion between unrelated kernel objects. A
> > use-after-free in any subsystem sharing slab pages with key_jar could
> > allow an attacker to reclaim a freed slot as a struct key, or corrupt
> > an existing key through a dangling pointer to a different type.
> > 
> > Add SLAB_NO_MERGE to ensure key_jar receives dedicated slab pages,
> > eliminating cross-cache attacks targeting struct key. The memory
> > overhead is minimal: with 32 objects per slab page and typical key
> > usage bounded by system keyring size, the cost of dedicated pages is
> > negligible. There is zero performance impact on the allocation hot
> > path.
> > 
> > This follows the precedent set by skbuff_head_cache (net/core/skbuff.c)
> > which uses SLAB_NO_MERGE for similar isolation requirements.
> > 
> > Signed-off-by: Mohammed EL Kadiri <med08elkadiri@gmail.com>
> 
> Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

Thank you.

has been applied

BR, Jarkko