APPLIED: [SRU][Xenial][CVE-2018-20856][PATCH] block: blk_init_allocated_queue() set q->fq as NULL in the fail case

[Khaled Elmously]

On 2019-08-02 10:11:28 , Connor Kuehl wrote:
> From: xiao jin <jin.xiao at intel.com>
> 
> CVE-2018-20856
> 
> 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 at vger.kernel.org>
> Reviewed-by: Ming Lei <ming.lei at redhat.com>
> Reviewed-by: Bart Van Assche <bart.vanassche at wdc.com>
> Signed-off-by: xiao jin <jin.xiao at intel.com>
> Signed-off-by: Jens Axboe <axboe at kernel.dk>
> (backported from commit 54648cf1ec2d7f4b6a71767799c45676a138ca24)
> [ Connor Kuehl: had to place the line from the patch in manually since
>   the patch context disagreed with what the routine looks like now
>   (different label, different return statement). Barely more involved
>   than an offset adjustment. ]
> Signed-off-by: Connor Kuehl <connor.kuehl at canonical.com>
> ---
>  block/blk-core.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index f83b9c2b6a14..a3e1f4fcb2e5 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -861,6 +861,7 @@ 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);
> -- 
> 2.20.1
> 
> 
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