linux-kernel - Re: [PATCH] cgroup/misc: Fix an overflow

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Date:   Mon, 17 Jul 2023 08:51:39 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Haitao Huang <haitao.huang@...ux.intel.com>
Cc:     jarkko@...nel.org, dave.hansen@...ux.intel.com,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        cgroups@...r.kernel.org, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, vipinsh@...gle.com,
        kai.huang@...el.com, reinette.chatre@...el.com,
        zhiquan1.li@...el.com, kristen@...ux.intel.com
Subject: Re: [PATCH] cgroup/misc: Fix an overflow

On Mon, Jul 17, 2023 at 11:47:19AM -0700, Haitao Huang wrote:
> The variable 'new_usage' in misc_cg_try_charge() may overflow if it
> becomes above INT_MAX. This was observed when I implement the new SGX
> EPC cgroup[1] as a misc cgroup and test on a platform with large SGX EPC
> sizes.
> 
> Change type of new_usage to long from int and check overflow.
> -	int new_usage;
> +	long new_usage;
>  
>  	if (!(valid_type(type) && cg && READ_ONCE(misc_res_capacity[type])))
>  		return -EINVAL;
> @@ -153,10 +153,10 @@ int misc_cg_try_charge(enum misc_res_type type, struct misc_cg *cg,
>  
>  	for (i = cg; i; i = parent_misc(i)) {
>  		res = &i->res[type];
> -
>  		new_usage = atomic_long_add_return(amount, &res->usage);
>  		if (new_usage > READ_ONCE(res->max) ||
> -		    new_usage > READ_ONCE(misc_res_capacity[type])) {
> +		    new_usage > READ_ONCE(misc_res_capacity[type]) ||
> +		    new_usage < 0) {

Applying to cgroup/for-6.6 (as none of the current users are affected by
this) but I think the right thing to do here is using explicit 64bit types
(s64 or u64) for the resource counters rather than depending on the long
width.

Thanks.

-- 
tejun