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

[Harry Yoo <harry@kernel.org>]

On 5/21/26 8:24 PM, Vladimir Zapolskiy wrote:
> 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.

Ah, nevermind! I totally misread the patch.
I thought it only addresses the symlink name.

>> 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.

Yeah, now I see :)

-- 
Cheers,
Harry / Hyeonggon