FAILED: patch "[PATCH] block: blk_init_allocated_queue() set q->fq as NULL in the" failed to apply to 4.4-stable tree

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: xiao jin <[email protected]>
Date: Mon, 30 Jul 2018 14:11:12 +0800
Subject: [PATCH] block: blk_init_allocated_queue() set q->fq as NULL in the
fail case

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().

index 03a4ea93a5f3..23cd1b7770e7 100644
@@ -1184,6 +1184,7 @@ int blk_init_allocated_queue(struct request_queue *q)
 		q->exit_rq_fn(q, q->fq->flush_rq);
 out_free_flush_queue:
 	blk_free_flush_queue(q->fq);
+	q->fq = NULL;
 	return -ENOMEM;
 }
 EXPORT_SYMBOL(blk_init_allocated_queue);