linux-kernel - Re: [Devel] Re: [PATCH] Fix user struct leakage with locked IPC shem segment

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, 17 Jul 2007 13:07:55 +0400
From:	Kirill Korotaev <dev@...ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Pavel Emelianov <xemul@...nvz.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...nvz.org
Subject: Re: [Devel] Re: [PATCH] Fix user struct leakage with locked IPC shem
 segment

Andrew Morton wrote:
> On Mon, 16 Jul 2007 16:24:12 +0400
> Pavel Emelianov <xemul@...nvz.org> wrote:
> 
> 
>>When user locks an ipc shmem segmant with SHM_LOCK ctl and the
>>segment is already locked the shmem_lock() function returns 0. 
>>After this the subsequent code leaks the existing user struct:
> 
> 
> I'm curious.  For the past few months, people@...nvz.org have discovered
> (and fixed) an ongoing stream of obscure but serious and quite
> long-standing bugs.

thanks a lot :@)

> How are you discovering these bugs?

Not sure what to answer :) Just trying to do our best.

This bug was thought over by Pavel for about 3 month after a single
uid leak in container was detected by beancounters' kernel memory accounting...

>>== ipc/shm.c: sys_shmctl() ==
>>     ...
>>     err = shmem_lock(shp->shm_file, 1, user);
>>     if (!err) {
>>          shp->shm_perm.mode |= SHM_LOCKED;
>>          shp->mlock_user = user;
>>     }
>>     ...
>>==
>>
>>Other results of this are:
>>1. the new shp->mlock_user is not get-ed and will point to freed
>>   memory when the task dies.
> 
> 
> That sounds fairly serious - can this lead to memory corruption and crashes?

Yes it can. According to Pavel when the shmem segment is destroyed it
puts the mlock_user pointer, which can already be stalled.

Kirill
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/