Messages in this thread | | | Date | Tue, 13 May 2008 09:12:07 -0400 | From | Mathieu Desnoyers <> | Subject | Re: System call audit |
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* David Woodhouse (dwmw2@infradead.org) wrote: > On Tue, 2008-05-13 at 08:51 -0400, Mathieu Desnoyers wrote: > > * David Woodhouse (dwmw2@infradead.org) wrote: > > > On Mon, 2008-05-12 at 20:06 -0400, Mathieu Desnoyers wrote: > > > > Hi David, > > > > > > > > As I am looking into the system-wide system call tracing problem, I > > > > start to wonder how auditsc deals with the fact that user-space could > > > > concurrently change the content referred to by the __user pointers. > > > > > > In general we have to copy the content into kernel space, audit it, and > > > then act on it from there. See the explanation on the IPC audit patch at > > > http://lwn.net/Articles/125350/ for example. > > > > > > Auditing one thing and then acting on another would be simply broken. > > > > > > > This would be the case for execve. If we create a program with two > > > > thread; one is executing execve syscalls and the other thread would be > > > > modifying the userspace string containing the name of the program to > > > > execute. > > > > > > I was going to suggest that that attack vector won't work, because > > > execve() kills all threads. But all you have to do to avoid that is put > > > the data in question into a shared writable mmap and modify it from > > > another _process_. And in fact I suspect there's a combination of CLONE_ > > > flags which would avoid the thread-killing behaviour anyway. > > > > > > > Even better : if execve fails, it doesn't kill the threads. Therefore, > > all we have to do is to busy-loop doing failing execve() calls and > > atomically change the string to what we want to be executed. Can anyone > > test the sample snippet in a context where executing /bin/bash is > > disallowed on a SMP system ? I don't have a selinux setup handy. > > You were talking about audit earlier. Now you seem to be talking about > selinux. >
I thought selinux did hook into syscall audit ? (sorry, I am new to the kernel auditing field) The race I refer to is in the auditsc.c kernel code, so syscall audit would be the one I am talking about. I refer to selinux here just because, as of my understanding, it happens to be one module-based callback which can hook on syscall audit.
Mathieu
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