linux-kernel - Re: [PATCH v2 1/1] mm: Fix the uninitialized use in overcommit_policy

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Date:   Thu, 23 Sep 2021 01:56:27 +0000
From:   "chenjun (AM)" <chenjun102@...wei.com>
To:     Feng Tang <feng.tang@...el.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "Xiangrui (Euler)" <rui.xiang@...wei.com>
Subject: Re: [PATCH v2 1/1] mm: Fix the uninitialized use in
 overcommit_policy_handler

Hi Tang,

在 2021/9/22 23:34, Feng Tang 写道:
> Hi Jun,
> 
> On Wed, Sep 22, 2021 at 01:41:22AM +0000, Chen Jun wrote:
>> An unexpected value of /proc/sys/vm/panic_on_oom we will get,
>> after running the following program.
>>
>> int main()
>> {
>>      int fd = open("/proc/sys/vm/panic_on_oom", O_RDWR)
> 
> should this be "/proc/sys/vm/overcommit_memory"
> 

Sorry, that is my mistake, I will correct it in v3. Thanks.

>>      write(fd, "1", 1);
>>      write(fd, "2", 1);
>>      close(fd);
>> }
>>
>> write(fd, "2", 1) will pass *ppos = 1 to proc_dointvec_minmax.
>> proc_dointvec_minmax will return 0 without setting new_policy.
>>
>> t.data = &new_policy;
>> ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos)
>>        -->do_proc_dointvec
>>           -->__do_proc_dointvec
>>                if (write) {
>>                  if (proc_first_pos_non_zero_ignore(ppos, table))
>>                    goto out;
>>
>> sysctl_overcommit_memory = new_policy;
>>
>> so sysctl_overcommit_memory will be set to an uninitialized value.
>>
>> Check whether new_policy has been changed by proc_dointvec_minmax.
>   
> Other than the nit above, it looks good to me, thanks!
> 
> Reviewed-by: Feng Tang <feng.tang@...el.com>
> 
>> Fixes: 56f3547bfa4d ("mm: adjust vm_committed_as_batch according to vm overcommit policy"
>> Signed-off-by: Chen Jun <chenjun102@...wei.com>
>> ---
>>
>> v2:
>>    * Check whether new_policy has been changed by proc_dointvec_minmax.
>>
>>   mm/util.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/util.c b/mm/util.c
>> index 4ddb6e186dd5..d5be67771850 100644
>> --- a/mm/util.c
>> +++ b/mm/util.c
>> @@ -756,7 +756,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
>>   		size_t *lenp, loff_t *ppos)
>>   {
>>   	struct ctl_table t;
>> -	int new_policy;
>> +	int new_policy = -1;
>>   	int ret;
>>   
>>   	/*
>> @@ -774,7 +774,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
>>   		t = *table;
>>   		t.data = &new_policy;
>>   		ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
>> -		if (ret)
>> +		if (ret || new_policy == -1)
>>   			return ret;
>>   
>>   		mm_compute_batch(new_policy);
>> -- 
>> 2.17.1
>>
> 


-- 
Regards
Chen Jun