Re: [PATCH] mm/slab: fix probable issue of dentries registration under /sys/kernel/slab

[Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>]

Harry,

On 5/20/26 06:42, Harry Yoo wrote:
> 
> 
> On 5/20/26 10:10 AM, Vladimir Zapolskiy wrote:
>> L2TP/IP and L2TP/IPv6 protocol names contain a slash symbol, however these
>> names are blindly used as symlinks to slab cache objects registered under
>> /sys/kernel/slab. This kind of symlink creation is successful, but its
>> dentry is obviously broken, as well it breaks the access to the list of
>> /sys/kernel/slab dentries.
> 
> Oops. I just loaded l2tp_ip module and it indeed broke it.
> 
> $ ls
> ls: reading directory '.': Input/output error
> :0000136/                        kmalloc-rnd-01-16/   kmalloc-rnd-15-32/
> :0000192/                        kmalloc-rnd-02-512/  memdup_user-32/
> :0000560/                        kmalloc-rnd-06-192/  memdup_user-4k/
> :0000768/                        kmalloc-rnd-06-512/  pde_opener@
> :a-0000168/                      kmalloc-rnd-07-4k/   pidfs_xattr_cache@
> :A-0000184/                      kmalloc-rnd-11-8/    RAWv6/
> audit_buffer@                    kmalloc-rnd-11-96/   rpc_inode_cache/
> configfs_dir_cache@              kmalloc-rnd-12-4k/   task_delay_info@
> ecryptfs_global_auth_tok_cache@  kmalloc-rnd-13-128/  TCPv6/
> fscache_cookie_jar@              kmalloc-rnd-14-96/
> io_kiocb/                        kmalloc-rnd-15-2k/
> 
>> Likely L2TP protocol renames cannot be done, since the defined protocol
>> names are exposed over /proc/net/protocols for years, but the symlink
>> names can be renamed, because they are yet to be properly created, and
>> this should be eventually done by this change.
>>
>> The problem manifests itself, if CONFIG_L2TP_IP build symbol is selected.
>>
>> Fixes: 81819f0fc8285 ("SLUB core")
>> Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
>> ---
> 
> There is also a debugfs feature that would cause a similar issue.

thank you for review, I've just sent v2 fixing __kmem_cache_create_args()
side. As for debugfs I haven't reproduced any similar issue, please give
me a clue here, also likely any non-slab changes should be done separately.

> Can we replace '/' in the cache name, without renaming the protocol name?
> 

I believe that's exactly how it's done, the protocol name is left unchanged.

-- 
Best wishes,
Vladimir