Re: [PATCH] padata: do not leak refcount in reorder_work

[Chen Ridong]

On 2025/5/19 1:45, Dominik Grzegorzek wrote:
> A recent patch that addressed a UAF introduced a reference count leak:
> the parallel_data refcount is incremented unconditionally, regardless
> of the return value of queue_work(). If the work item is already queued,
> the incremented refcount is never decremented.
> 
> Fix this by checking the return value of queue_work() and decrementing
> the refcount when necessary.
> 
> Resolves:
> 
> Unreferenced object 0xffff9d9f421e3d80 (size 192):
>   comm "cryptomgr_probe", pid 157, jiffies 4294694003
>   hex dump (first 32 bytes):
>     80 8b cf 41 9f 9d ff ff b8 97 e0 89 ff ff ff ff  ...A............
>     d0 97 e0 89 ff ff ff ff 19 00 00 00 1f 88 23 00  ..............#.
>   backtrace (crc 838fb36):
>     __kmalloc_cache_noprof+0x284/0x320
>     padata_alloc_pd+0x20/0x1e0
>     padata_alloc_shell+0x3b/0xa0
>     0xffffffffc040a54d
>     cryptomgr_probe+0x43/0xc0
>     kthread+0xf6/0x1f0
>     ret_from_fork+0x2f/0x50
>     ret_from_fork_asm+0x1a/0x30
> 
> Fixes: dd7d37ccf6b1 ("padata: avoid UAF for reorder_work")
> Signed-off-by: Dominik Grzegorzek <dominik.grzegorzek@xxxxxxxxxx>
> ---
>  kernel/padata.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/padata.c b/kernel/padata.c
> index b3d4eacc4f5d..7eee94166357 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -358,7 +358,8 @@ static void padata_reorder(struct parallel_data *pd)
>  		 * To avoid UAF issue, add pd ref here, and put pd ref after reorder_work finish.
>  		 */
>  		padata_get_pd(pd);
> -		queue_work(pinst->serial_wq, &pd->reorder_work);
> +		if (!queue_work(pinst->serial_wq, &pd->reorder_work))
> +			padata_put_pd(pd);
>  	}
>  }
>  

Thank you. I missed this case.
LGTM

Thanks,
Ridong