netdev - Re: [PATCH v2] rps: fix insufficient bounds checking in store_rps_dev_flow_table

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Date:	Fri, 23 Dec 2011 05:10:14 +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 v2] rps: fix insufficient bounds checking in
 store_rps_dev_flow_table_cnt()

Le jeudi 22 décembre 2011 à 18:35 -0500, Xi Wang a écrit :
> Setting a large rps_flow_cnt like (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 replaces the magic number (1 << 30) with a symbolic bound.
> 
> Suggested-by: Eric Dumazet <eric.dumazet@...il.com>
> Signed-off-by: Xi Wang <xi.wang@...il.com>
> ---
>  net/core/net-sysfs.c |    7 +++++--
>  1 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index c71c434..385aefe 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -665,11 +665,14 @@ static ssize_t store_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
>  	if (count) {
>  		int i;
>  
> -		if (count > 1<<30) {
> +		if (count > INT_MAX)
> +			return -EINVAL;
> +		count = roundup_pow_of_two(count);
> +		if (count > (ULONG_MAX - sizeof(struct rps_dev_flow_table))

Oh well, you added a bug here, since count is "unsigned int"

Why mixing INT_MAX in the previous test and ULONG_MAX here ?


> +				/ sizeof(struct rps_dev_flow)) {
>  			/* Enforce a limit to prevent overflow */
>  			return -EINVAL;
>  		}
> -		count = roundup_pow_of_two(count);
>  		table = vmalloc(RPS_DEV_FLOW_TABLE_SIZE(count));
>  		if (!table)
>  			return -ENOMEM;


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