From: Stephen Smalley <sds@tycho.nsa.gov>
To: Topi Miettinen <toiwoton@gmail.com>,
Paul Moore <paul@paul-moore.com>,
Eric Paris <eparis@parisplace.org>,
James Morris <james.l.morris@oracle.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
"moderated list:SELINUX SECURITY MODULE" <selinux@tycho.nsa.gov>,
"open list:SECURITY SUBSYSTEM"
<linux-security-module@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: selinux: should execmem disable shmat(..., SHM_EXEC)?
Date: Thu, 27 Oct 2016 09:01:35 -0400 [thread overview]
Message-ID: <732d3c0d-a7d1-22b3-d468-b0d399ba56ff@tycho.nsa.gov> (raw)
In-Reply-To: <3f453e5e-e70c-f00d-9b5b-f09addd04ada@gmail.com>
On 10/26/2016 04:31 PM, Topi Miettinen wrote:
> Hi,
>
> Maybe this is a stupid question and I didn't test this with SELinux, but
> it looks to me that SELinux execmem does not prevent process from
> getting writable and executable memory mappings by using shmat(...,
> SHM_EXEC). Shouldn't this be blocked by execmem, I suppose it is there
> to prevent this kind of memory access?
>
> Here's a test program:
> #include <sys/ipc.h>
> #include <sys/shm.h>
>
> int main(void) {
> int shmid;
> char *execmem;
> void (*fn)(void);
>
> shmid = shmget(IPC_PRIVATE, 4096, IPC_CREAT | 0777);
> execmem = shmat(shmid, 0, SHM_EXEC);
> shmctl(shmid, IPC_RMID, 0);
> *execmem = 0xc3; // retq
> fn = (void (*)(void))execmem;
> fn();
> shmdt(execmem);
> }
>
> -Topi
>
The test program fails with a seg fault and a SELinux avc denial for
execmem permission when run in a domain that lacks execmem permission.
Thanks though for the test; I'll add it to the selinux testsuite to
ensure we don't regress in this area.
prev parent reply other threads:[~2016-10-27 14:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-26 20:31 selinux: should execmem disable shmat(..., SHM_EXEC)? Topi Miettinen
2016-10-27 13:01 ` Stephen Smalley [this message]
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