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

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Date:   Mon, 17 Jul 2023 18:55:32 +0000
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "Haitao Huang" <haitao.huang@...ux.intel.com>,
        <dave.hansen@...ux.intel.com>, <tj@...nel.org>,
        <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>
Cc:     <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 6:47 PM UTC, 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.
>
> Fixes: a72232eabdfcf ("cgroup: Add misc cgroup controller")
> Signed-off-by: Haitao Huang <haitao.huang@...ux.intel.com>
>
> [1] https://lore.kernel.org/linux-sgx/20230712230202.47929-1-haitao.huang@linux.intel.com/
> ---
>  kernel/cgroup/misc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/cgroup/misc.c b/kernel/cgroup/misc.c
> index fe3e8a0eb7ed..ff9f900981a3 100644
> --- a/kernel/cgroup/misc.c
> +++ b/kernel/cgroup/misc.c
> @@ -143,7 +143,7 @@ int misc_cg_try_charge(enum misc_res_type type, struct misc_cg *cg,
>  	struct misc_cg *i, *j;
>  	int ret;
>  	struct misc_res *res;
> -	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];
> -

This is extra noise in the patch, please remove the change.

>  		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) {
>  			ret = -EBUSY;
>  			goto err_charge;
>  		}
> -- 
> 2.25.1

BR, Jarkko