Re: [PATCH 3.18.y 4.4.y 4.9.y] block: blk_init_allocated_queue() set q->fq as NULL in the fail case

[Greg KH]

On Thu, Aug 08, 2019 at 03:28:19AM +0100, Alessio Balsini wrote:
> From: xiao jin <jin.xiao@xxxxxxxxx>
> 
> commit 54648cf1ec2d7f4b6a71767799c45676a138ca24 upstream.
> 
> We find the memory use-after-free issue in __blk_drain_queue()
> on the kernel 4.14. After read the latest kernel 4.18-rc6 we
> think it has the same problem.
> 
> Memory is allocated for q->fq in the blk_init_allocated_queue().
> If the elevator init function called with error return, it will
> run into the fail case to free the q->fq.
> 
> Then the __blk_drain_queue() uses the same memory after the free
> of the q->fq, it will lead to the unpredictable event.
> 
> The patch is to set q->fq as NULL in the fail case of
> blk_init_allocated_queue().
> 
> Fixes: commit 7c94e1c157a2 ("block: introduce blk_flush_queue to drive flush machinery")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
> Reviewed-by: Bart Van Assche <bart.vanassche@xxxxxxx>
> Signed-off-by: xiao jin <jin.xiao@xxxxxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> Signed-off-by: Alessio Balsini <balsini@xxxxxxxxxxx>
> ---
>  block/blk-core.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 50d77c90070d..7662f97dded6 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -870,6 +870,7 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
>  
>  fail:
>  	blk_free_flush_queue(q->fq);
> +	q->fq = NULL;
>  	return NULL;
>  }
>  EXPORT_SYMBOL(blk_init_allocated_queue);
> -- 
> 2.22.0.770.g0f2c4a37fd-goog
> 

Guenter sent this backport a day before you did, so I took his version
and added your s-o-b to it.

thanks,

greg k-h