Re: [PATCH] Forcing subclasses to have same name pointer as their parent class

From: Boqun Feng
Date: Wed Jul 03 2024 - 18:46:38 EST


Hi,

On Thu, Jul 04, 2024 at 03:32:24AM +0300, botta633 wrote:
> Preventing Lockdep_set_subclass from creating a new instance of the
> string literal. Hence, we will always have the class->name. This
> prevents kernel panics when locking up a lock class while comparing
> class locks and class names.

Good catch! Thanks.

>
>

Please remove the extra blank line here.

> Signed-off-by: botta633 <bottaawesome633@xxxxxxxxx>

Do you mind putting your real name here? Besides, IIUC, this is fixing:

https://syzkaller.appspot.com/bug?extid=7f4a6f7f7051474e40ad

, right? If so, there are some more things:

* Copy ext4 and syzkaller people, so that you could get more
tests.

* Since this is a bug fix, could you please figure out which
commit introduces the issue, so that you can put a correct
"Fixes:" tag along with your signed-off-by?

* Since the issue was reported by syzkaller, you should put their
"Reported-by" tag, they have an example in the website I paste
above.

* Please also Cc stable mail list so that the fix can be
backported, you can find the information on "Cc: stable" tag at:

https://docs.kernel.org/process/stable-kernel-rules.html

* Last but not the least, could you try to add a test case in
lib/locking-selftest.c to ensure the issue you fixed won't
happen again? This could be tricky, since you will need to fight
against the compiler to generate two string literals with the
same content.

[Cc ext4 and syzkaller]

Regards,
Boqun

> ---
> include/linux/lockdep.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 08b0d1d9d78b..df8fa5929de7 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -173,7 +173,7 @@ static inline void lockdep_init_map(struct lockdep_map *lock, const char *name,
> (lock)->dep_map.lock_type)
>
> #define lockdep_set_subclass(lock, sub) \
> - lockdep_init_map_type(&(lock)->dep_map, #lock, (lock)->dep_map.key, sub,\
> + lockdep_init_map_type(&(lock)->dep_map, (lock)->dep_map.name, (lock)->dep_map.key, sub,\
> (lock)->dep_map.wait_type_inner, \
> (lock)->dep_map.wait_type_outer, \
> (lock)->dep_map.lock_type)
> --
> 2.45.2
>