linux-ext4 - Re: [PATCH] Forcing subclasses to have same name pointer as their parent class

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Message-ID: <ZoXUgdUkD-GtKfKJ@boqun-archlinux>
Date: Wed, 3 Jul 2024 15:45:21 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: botta633 <bottaawesome633@...il.com>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>, linux-ext4@...r.kernel.org,
	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	syzkaller@...glegroups.com, "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH] Forcing subclasses to have same name pointer as their
 parent class

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@...il.com>

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
>