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

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Date:   Mon, 17 Jul 2023 15:19:38 -0500
From:   "Haitao Huang" <haitao.huang@...ux.intel.com>
To:     "Jarkko Sakkinen" <jarkko@...nel.org>, "Tejun Heo" <tj@...nel.org>,
        "Haitao Huang" <haitao.huang@...ux.intel.com>
Cc:     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, 17 Jul 2023 14:01:03 -0500, Haitao Huang  
<haitao.huang@...ux.intel.com> wrote:

> On Mon, 17 Jul 2023 13:57:59 -0500, Tejun Heo <tj@...nel.org> wrote:
>
>> On Mon, Jul 17, 2023 at 06:55:32PM +0000, Jarkko Sakkinen wrote:
>>> 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.
>>
>> Lemme just revert it. Haitao, can you instead make the resource  
>> counters and
>> all related variables explicit 64bit instead?
>>
>
> Will do.

Actually, we are using atomic_long_t for 'current' which is the same width  
as long defined by arch/compiler. So new_usage should be long to be  
consistent?

ditto for event counter. Only max is plain unsigned long but I think it is  
also OK as it only compared with 'current' without any arithmetic ops  
involved.
Did I miss something here?
Thanks
Haitao