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  PHC 
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Thu, 22 May 2014 16:01:20 +0300
From:	Marian Marinov <>
To:	Manfred Spraul <>,
	Davidlohr Bueso <>
	Greg KH <>,
	"" <>,
	Linux Containers <>
Subject: Re: [PATCH] IPC initialize shmmax and shmall from the current value
 not the default

Hash: SHA1

On 05/05/2014 10:59 PM, Marian Marinov wrote:
> On 05/04/2014 02:17 PM, Manfred Spraul wrote:
>> Hi Marian,
>> Note: The limits will soon be increased to (nearly) ULONG_MAX. I.e.: If you propose the patch because you are
>> running into issues with a too small SEMMAX after an unshare(CLONE_NEWIPC), then this will be fixed soon.
>> On 05/04/2014 01:53 AM, Davidlohr Bueso wrote:
>>> On Sun, 2014-05-04 at 01:48 +0300, Marian Marinov wrote:
>>>> When we are creating new IPC namespace that should be cloned from the current namespace it is a good idea to
>>>> copy the values of the current shmmax and shmall to the new namespace.
>> The idea sounds reasonable: If an admin has reduced the limits, then the reduction should also apply after a
>> unshare(CLONE_NEWIPC).
>> But: Your patch doesn't use the current shmmax, it uses the shmmax from init_ipc_ns. Would it be possible to use
>> the current values?
> In my tests it worked exactly as expected. Here is an example:
> [root@sp2 ~]# sysctl -a|grep shmmax kernel.shmmax = 68719476736 [root@sp2 ~]# lxc-attach -n cent_plain 
> [root@...alhost ~]# sysctl -a|grep shmmax kernel.shmmax = 68719476736 [root@...alhost ~]# halt [root@sp2 ~]# sysctl
> -a|grep shmmax kernel.shmmax = 68719476736 [root@sp2 ~]# sysctl kernel.shmmax=34359738368 kernel.shmmax =
> 34359738368 [root@sp2 ~]# lxc-start -n cent_plain -d [root@sp2 ~]# lxc-attach -n cent_plain [root@...alhost ~]#
> sysctl -a|grep shmmax kernel.shmmax = 34359738368 [root@...alhost ~]#
> So it seams to work as expected :)
> It works because wen you setup a new shmmax limit it is actually the limit in the init_ipc_ns. So when we are
> creating a new ipc_ns its ok to copy the values from init_ipc_ns.
> -Marian


So will there be any more comments on that?


>>> Why is this a good idea?
>>> This would break userspace that relies on the current behavior. Furthermore we've recently changed the default
>>> value of both these limits to be as large as you can get, thus deprecating them. I don't like the idea of this
>>> being replaced by namespaces.
>> Davidlohr: We are not deprecating them, we make the default huge. The limits should stay as usable as they were.
>> With regards to breaking user space, I must think about it a bit more. Right now, each new namespace starts with
>> SEMMAX=32MB, i.e. an often unusable default.
>> -- Manfred

- -- 
Marian Marinov
Founder & CEO of 1H Ltd.
ICQ: 7556201
Mobile: +359 886 660 270
Version: GnuPG v2.0.22 (GNU/Linux)

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists