Re: [PATCH V2] blk-mq: avoid sysfs buffer overflow by too many CPU cores

[Bart Van Assche <bvanassche@acm.org>]

On 8/15/19 7:54 PM, Ming Lei wrote:
> It is reported that sysfs buffer overflow can be triggered in case
> of too many CPU cores(>841 on 4K PAGE_SIZE) when showing CPUs in
> blk_mq_hw_sysfs_cpus_show().
> 
> So use cpumap_print_to_pagebuf() to print the info and fix the potential
> buffer overflow issue.
> 
> Cc: stable@vger.kernel.org
> Cc: Mark Ray <mark.ray@hpe.com>
> Cc: Greg KH <gregkh@linuxfoundation.org>
> Fixes: 676141e48af7("blk-mq: don't dump CPU -> hw queue map on driver load")
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>   block/blk-mq-sysfs.c | 15 +--------------
>   1 file changed, 1 insertion(+), 14 deletions(-)
> 
> diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
> index d6e1a9bd7131..4d0d32377ba3 100644
> --- a/block/blk-mq-sysfs.c
> +++ b/block/blk-mq-sysfs.c
> @@ -166,20 +166,7 @@ static ssize_t blk_mq_hw_sysfs_nr_reserved_tags_show(struct blk_mq_hw_ctx *hctx,
>   
>   static ssize_t blk_mq_hw_sysfs_cpus_show(struct blk_mq_hw_ctx *hctx, char *page)
>   {
> -	unsigned int i, first = 1;
> -	ssize_t ret = 0;
> -
> -	for_each_cpu(i, hctx->cpumask) {
> -		if (first)
> -			ret += sprintf(ret + page, "%u", i);
> -		else
> -			ret += sprintf(ret + page, ", %u", i);
> -
> -		first = 0;
> -	}
> -
> -	ret += sprintf(ret + page, "\n");
> -	return ret;
> +	return cpumap_print_to_pagebuf(true, page, hctx->cpumask);
>   }
>   
>   static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_nr_tags = {

Although this patch looks fine to me, shouldn't this attribute be 
documented under Documentation/ABI/?

Thanks,

Bart.