Re: [PATCH] workqueue: fix null-ptr-deref on __alloc_workqueue() error

[Sergey Senozhatsky <senozhatsky@chromium.org>]

On (24/08/15 16:02), Sergey Senozhatsky wrote:
> wq->lockdep_map is set only after __alloc_workqueue()
> successfully returns. However, on its error path
> __alloc_workqueue() may call destroy_workqueue() which
> expects wq->lockdep_map to be already set, which results
> in a null-ptr-deref in touch_wq_lockdep_map().
> 
> Add a simple NULL-check to touch_wq_lockdep_map().
> 
> Oops: general protection fault, probably for non-canonical address
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> RIP: 0010:__lock_acquire+0x81/0x7800
> [..]
> Call Trace:
>  <TASK>
>  ? __die_body+0x66/0xb0
>  ? die_addr+0xb2/0xe0
>  ? exc_general_protection+0x300/0x470
>  ? asm_exc_general_protection+0x22/0x30
>  ? __lock_acquire+0x81/0x7800
>  ? mark_lock+0x94/0x330
>  ? __lock_acquire+0x12fd/0x7800
>  ? __lock_acquire+0x3439/0x7800
>  lock_acquire+0x14c/0x3e0
>  ? __flush_workqueue+0x167/0x13a0
>  ? __init_swait_queue_head+0xaf/0x150
>  ? __flush_workqueue+0x167/0x13a0
>  __flush_workqueue+0x17d/0x13a0
>  ? __flush_workqueue+0x167/0x13a0
>  ? lock_release+0x50f/0x830
>  ? drain_workqueue+0x94/0x300
>  drain_workqueue+0xe3/0x300
>  destroy_workqueue+0xac/0xc40
>  ? workqueue_sysfs_register+0x159/0x2f0
>  __alloc_workqueue+0x1506/0x1760
>  alloc_workqueue+0x61/0x150
> ...
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> ---
>  kernel/workqueue.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index bfeeefeee332..59bd2c1e55af 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -3870,6 +3870,9 @@ static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
>  static void touch_wq_lockdep_map(struct workqueue_struct *wq)
>  {
>  #ifdef CONFIG_LOCKDEP
> +	if (unlikely(!wq->lockdep_map))
> +		return;
> +
>  	if (wq->flags & WQ_BH)
>  		local_bh_disable();

Oh, okay, so this is related to [1]

	workqueue: Split alloc_workqueue into internal function and lockdep init

Cc-ing Matthew on this.

[1] https://lore.kernel.org/all/20240809222827.3211998-2-matthew.brost@intel.com/