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 <[email protected]>
Acked-by: Vlastimil Babka (SUSE) <[email protected]> > --- > security/keys/key.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/security/keys/key.c b/security/keys/key.c > index 3bbdde778631..592b65cf8539 100644 > --- a/security/keys/key.c > +++ b/security/keys/key.c > @@ -1275,7 +1275,7 @@ void __init key_init(void) > { > /* allocate a slab in which we can store keys */ > key_jar = kmem_cache_create("key_jar", sizeof(struct key), > - 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); > + 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_NO_MERGE, > NULL); > > /* add the special key types */ > list_add_tail(&key_type_keyring.link, &key_types_list);
