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

[Harry Yoo]

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@xxxxxxxxxx>
> ---

There is also a debugfs feature that would cause a similar issue.
Can we replace '/' in the cache name, without renaming the protocol name?

--
Cheers,
Harry / Hyeonggon