linux-kernel - Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 27 Mar 2018 14:38:11 -0400
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     adobriyan@...il.com, willy@...radead.org, mguzik@...hat.com,
        gorcunov@...nvz.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and
 env_start|end in mm_struct



On 3/27/18 2:29 AM, Michal Hocko wrote:
> On Tue 27-03-18 02:20:39, Yang Shi wrote:
> [...]
> The patch looks reasonable to me. Maybe it would be better to be more
> explicit about the purpose of the patch. As others noticed, this alone
> wouldn't solve the mmap_sem contention issues. I _think_ that if you
> were more explicit about the mmap_sem abuse it would trigger less
> questions.

Yes, sure.

>
> I have just one more question. Now that you are touching this area,
> would you be willing to remove the following ugliness?
>
>> diff --git a/kernel/sys.c b/kernel/sys.c
>> index f2289de..17bddd2 100644
>> --- a/kernel/sys.c
>> +++ b/kernel/sys.c
>> @@ -1959,7 +1959,7 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
>>   			return error;
>>   	}
>>   
>> -	down_write(&mm->mmap_sem);
>> +	down_read(&mm->mmap_sem);
> Why do we need to hold mmap_sem here and call find_vma, when only
> PR_SET_MM_ENV_END: is consuming it? I guess we can replace it wit the
> new lock and take the mmap_sem only for PR_SET_MM_ENV_END.

Actually, I didn't think of why. It looks prctl_set_mm() checks if vma 
does exist when it tries to set stack_start, argv_* and env_*, btw not 
only env_end.

Cyrill may be able to give us some hint since C/R is the main user of 
this API.

Yang

>
> Thanks!