netdev - Re: [PATCH] rps: fix insufficient bounds checking in store_rps_dev_flow_table

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Date:	Wed, 21 Dec 2011 20:22:24 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Xi Wang <xi.wang@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] rps: fix insufficient bounds checking in
 store_rps_dev_flow_table_cnt()

Le mercredi 21 décembre 2011 à 13:50 -0500, Xi Wang a écrit :
> Setting a large rps_flow_cnt like 1073741824 (1 << 30) on 32-bit
> platform will cause a kernel oops due to insufficient bounds checking.
> 
> 	if (count > 1<<30) {
> 		/* Enforce a limit to prevent overflow */
> 		return -EINVAL;
> 	}
> 	count = roundup_pow_of_two(count);
> 	table = vmalloc(RPS_DEV_FLOW_TABLE_SIZE(count));
> 
> Note that the macro RPS_DEV_FLOW_TABLE_SIZE(count) is defined as:
> 
> 	... + (count * sizeof(struct rps_dev_flow))
> 
> where sizeof(struct rps_dev_flow) is 8.  (1 << 30) * 8 will overflow
> 32 bits.  This patch changes the upper bound to (1 << 28).
> 
> Signed-off-by: Xi Wang <xi.wang@...il.com>
> ---
>  net/core/net-sysfs.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index c71c434..f53a947 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -665,7 +665,7 @@ static ssize_t store_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
>  	if (count) {
>  		int i;
>  
> -		if (count > 1<<30) {
> +		if (count > 1<<28) {
>  			/* Enforce a limit to prevent overflow */
>  			return -EINVAL;
>  		}


Really, you should remove this magic number and use instead

(INT_MAX - RPS_DEV_FLOW_TABLE_SIZE(0)) / sizeof(struct rps_dev_flow)

Or something like that, because next time we add a field in
rps_dev_flow, test will be obsolete.



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