[PATCH v4 1/2] locking/lockdep: Forcing subclasses to have same name pointer as their parent class

[PATCH v4 1/2] locking/lockdep: Forcing subclasses to have same name pointer as their parent class

[botta633]

From: Ahmed Ehab <bottaawesome633@gmail.com>

Preventing lockdep_set_subclass from creating a new instance of the
string literal. Hence, we will always have the same class->name among
parent and subclasses. This prevents kernel panics when looking up a
lock class while comparing class locks and class names.

Reported-by: <syzbot+7f4a6f7f7051474e40ad@syzkaller.appspotmail.com>
Fixes: de8f5e4f2dc1f ("lockdep: Introduce wait-type checks")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ahmed Ehab <bottaawesome633@gmail.com>
---
 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

Re: [PATCH v4 1/2] locking/lockdep: Forcing subclasses to have same name pointer as their parent class

[Greg KH]

On Mon, Jul 15, 2024 at 09:34:46AM +0300, botta633 wrote:
> From: Ahmed Ehab <bottaawesome633@gmail.com>
> 
> Preventing lockdep_set_subclass from creating a new instance of the
> string literal. Hence, we will always have the same class->name among
> parent and subclasses. This prevents kernel panics when looking up a
> lock class while comparing class locks and class names.
> 
> Reported-by: <syzbot+7f4a6f7f7051474e40ad@syzkaller.appspotmail.com>
> Fixes: de8f5e4f2dc1f ("lockdep: Introduce wait-type checks")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Ahmed Ehab <bottaawesome633@gmail.com>
> ---
>  include/linux/lockdep.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- This looks like a new version of a previously submitted patch, but you
  did not list below the --- line any changes from the previous version.
  Please read the section entitled "The canonical patch format" in the
  kernel file, Documentation/process/submitting-patches.rst for what
  needs to be done here to properly describe this.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.

thanks,

greg k-h's patch email bot

[PATCH v4 2/2] locking/lockdep: Testing lock class and subclass got the same name pointer

[botta633]

From: Ahmed Ehab <bottaawesome633@gmail.com>

Checking if the lockdep_map->name will change when setting the subclass.
It shouldn't change so that the lock class and subclass will have the same
name

Reported-by: <syzbot+7f4a6f7f7051474e40ad@syzkaller.appspotmail.com>
Fixes: de8f5e4f2dc1f ("lockdep: Introduce wait-type checks")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ahmed Ehab <bottaawesome633@gmail.com>
---
 lib/locking-selftest.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index 6f6a5fc85b42..aeed613799ca 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -2710,6 +2710,25 @@ static void local_lock_3B(void)
 
 }
 
+ /** 
+  * after setting the subclass the lockdep_map.name changes
+  * if we initialize a new string literal for the subclass
+  * we will have a new name pointer
+  */
+static void class_subclass_X1_name_test(void)
+{
+	printk("  --------------------------------------------------------------------------\n");
+	printk("  | class and subclass name test|\n");
+	printk("  ---------------------\n");
+	const char *name_before_setting_subclass = rwsem_X1.dep_map.name;
+	const char *name_after_setting_subclass;
+
+	WARN_ON(!rwsem_X1.dep_map.name);
+	lockdep_set_subclass(&rwsem_X1, 1);
+	name_after_setting_subclass = rwsem_X1.dep_map.name;
+	WARN_ON(name_before_setting_subclass != name_after_setting_subclass);
+}
+
 static void local_lock_tests(void)
 {
 	printk("  --------------------------------------------------------------------------\n");
@@ -2916,6 +2935,8 @@ void locking_selftest(void)
 
 	local_lock_tests();
 
+	class_subclass_X1_name_test();
+
 	print_testname("hardirq_unsafe_softirq_safe");
 	dotest(hardirq_deadlock_softirq_not_deadlock, FAILURE, LOCKTYPE_SPECIAL);
 	pr_cont("\n");
-- 
2.45.2

[PATCH v4 1/2] locking/lockdep: Forcing subclasses to have same name pointer as their parent class

[botta633]

From: Ahmed Ehab <bottaawesome633@gmail.com>

Preventing lockdep_set_subclass from creating a new instance of the
string literal. Hence, we will always have the same class->name among
parent and subclasses. This prevents kernel panics when looking up a
lock class while comparing class locks and class names.

Reported-by: <syzbot+7f4a6f7f7051474e40ad@syzkaller.appspotmail.com>
Fixes: de8f5e4f2dc1f ("lockdep: Introduce wait-type checks")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ahmed Ehab <bottaawesome633@gmail.com>
---
v3->v4:
    - Fixed subject line truncation.

 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

Re: [PATCH v4 1/2] locking/lockdep: Forcing subclasses to have same name pointer as their parent class

[Boqun Feng]

On Mon, Jul 15, 2024 at 04:26:37PM +0300, botta633 wrote:
> From: Ahmed Ehab <bottaawesome633@gmail.com>
> 
> Preventing lockdep_set_subclass from creating a new instance of the
> string literal. Hence, we will always have the same class->name among
> parent and subclasses. This prevents kernel panics when looking up a
> lock class while comparing class locks and class names.
> 
> Reported-by: <syzbot+7f4a6f7f7051474e40ad@syzkaller.appspotmail.com>
> Fixes: de8f5e4f2dc1f ("lockdep: Introduce wait-type checks")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Ahmed Ehab <bottaawesome633@gmail.com>

This looks good to me.

Regards,
Boqun

> ---
> v3->v4:
>     - Fixed subject line truncation.
> 
>  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

Re: [PATCH v4 1/2] locking/lockdep: Forcing subclasses to have same name pointer as their parent class

[Boqun Feng]

Hi Ahmed,

Sorry I was missing some points on title and changelog, please see below
and refer to Documentation/process/maintainer-tip.rst:

The title needs to be something like:

	locking/lockdep: Avoid creating new name string literals in lockdep_set_subclass()

the title and the changlog needs to be in imperative mode.

On Mon, Jul 15, 2024 at 04:26:37PM +0300, botta633 wrote:
> From: Ahmed Ehab <bottaawesome633@gmail.com>
> 
> Preventing lockdep_set_subclass from creating a new instance of the


Same here, s/Preventing/Prevent, and when you reference a function, you
want to do "lockdep_set_subclass()" instead of "lockdep_set_subclass".


Besides, overall, you want to structure your changelog as follow:

Syzbot reports a problem that a warning will be triggered while
searching a lock class in look_up_lock_class().

// ^ the problem statement

The cause of the issue is that instead of the existing name of a
lock class, a new name (a string literal) is created and used by
lockdep_set_subclass(), and this results in two lock classes with the
same key but different address of the names, and a WARN_ONCE() is
triggered because of that in look_up_lock_class().

// ^ the analysis of the problem, you can merge the above two into one
// paragraph if that works for you.

To fix this, change lockdep_set_subclass() to use the existing name
instead of a new one. As a result no new name will be created by
lockdep_set_subclass(), hence the warning is avoided.

// ^ the fix.


Please send a new version if these make sense to you. The patch #2 also
needs some changes in the title and changelog, but since that's adding
a new test instead of fixing an issue, you could just write something
like:

Add a test case to ensure that no new name string literal will be
created in lockdep_set_subclass(), otherwise a warning will be triggered
in look_up_lock_class(). Add this to catch the problem in the future.


Thanks!

Regards,
Boqun

> string literal. Hence, we will always have the same class->name among
> parent and subclasses. This prevents kernel panics when looking up a
> lock class while comparing class locks and class names.
> 
> Reported-by: <syzbot+7f4a6f7f7051474e40ad@syzkaller.appspotmail.com>
> Fixes: de8f5e4f2dc1f ("lockdep: Introduce wait-type checks")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Ahmed Ehab <bottaawesome633@gmail.com>
> ---
> v3->v4:
>     - Fixed subject line truncation.
> 
>  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