From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com Sender: Vasiliy Kulikov Date: Fri, 17 Jun 2011 13:56:25 +0400 From: Vasiliy Kulikov Message-ID: <20110617095625.GA7627@albatros> References: <20110617083651.GA5625@albatros> <1308302957.2355.5.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1308302957.2355.5.camel@twins> Subject: [kernel-hardening] Re: How to temporary change 'current' (task) To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Ingo Molnar , kernel-hardening@lists.openwall.com List-ID: On Fri, Jun 17, 2011 at 11:29 +0200, Peter Zijlstra wrote: > On Fri, 2011-06-17 at 12:36 +0400, Vasiliy Kulikov wrote: > > I wonder whether there is a simple way to temporary switch 'current' to > > another task and then switch it back with minimum side effects? > > No. After a moment's thought, it would also break some synchronization that relies on some structures are accesses only from the current task. > > I need > > it to call "reversed" ptrace_may_access() with swapped current and > > target task. Introducing ptrace_task_may_access_me() would produce too > > much noise in LSM (it also needs reversed security_ptrace_access_check()), > > which is too loud for my needs. > > > > Specifically, I need it to filter taskstats and proc connector requests > > for a restriction of getting other processes' information: > > > > http://permalink.gmane.org/gmane.linux.kernel/1155354 > > > > As the check is handled in the context of the ptrace target process, > > ptrace_may_access() doesn't fit my needs. > > looking at __ptrace_may_access() it doesn't look too hard to make it > take two task arguments and use __task_cred() twice instead of > current_cred(). > > It of course needs extending security_ptrace_access_check() as well, but > that comes with the territory. Well, yes, but it implies pushing explicit ptrace actor into LSM modules. OK, it should be not as noisy as I initially thought - almost all current LSMs already use "current" as an explicit argument in theirs internal functions. Thank you, -- Vasiliy