Re: selinux_msg_queue_msgrcv() oops

[Stanislav Kinsbursky]

06.02.2013 23:51, Tommi Rantala ÐÐÑÐÑ:
> 2013/2/6 Stephen Smalley <sds@xxxxxxxxxxxxx>:
> > On 02/06/2013 10:21 AM, Tommi Rantala wrote:
> > > 2013/2/6 Stephen Smalley <sds@xxxxxxxxxxxxx>:
> > > > On 02/06/2013 07:56 AM, Tommi Rantala wrote:
> > > > > Hello,
> > > > >
> > > > > I'm hitting an oops in selinux_msg_queue_msgrcv() when fuzzing with
> > > > > Trinity as the root user (in a qemu VM):
> > > >
> > > >
> > > >
> > > > NULL msg->security at that point is a bug in the ipc subsystem; SELinux
> > > > is
> > > > just the messenger.  Normally msg->security is set for every allocated
> > > > msg
> > > > by load_msg() -> security_msg_msg_alloc() ->
> > > > selinux_msg_msg_alloc_security(), and freed/cleared upon free_msg() ->
> > > > security_msg_msg_free() -> selinux_msg_msg_free_security().  Looking
> > > > around,
> > > > I see copy_msg() introduced for checkpoint-restore initializes
> > > > dst->security
> > > > to NULL but never sets it properly?
> > >
> > >
> > > I am indeed building with CONFIG_CHECKPOINT_RESTORE=y, so your
> > > analysis seems to be correct.
> >
> >
> > (cc originator of the bug)
> >
> > If I am reading this correctly, then when the copy msg was created, a msg
> > security struct was already allocated
> > (prepare_copy->load_msg->security_msg_msg_alloc).  So having copy_msg()
> > clear dst->security is also a memory leak in addition to leading to this
> > oops.  Attached is a possible, un-tested fix.
>
> I can still reproduce the exact same oops with the patch applied. I
> also wanted to be sure that copy_msg() is called, so I added a warning
> there, but that never gets triggered. So I suppose the problem is not
> actually related to CONFIG_CHECKPOINT_RESTORE.

Hello.
Unfortunately, you are not the first one, who experience problems with Trinity running in KVM.

copy_msg() won't be called unless you'll specify the MSG_COPY flag in msgrcv() flags parameter.

Could you make a small investigation around the problem?
For example, does this problem appear, is you disable CONFIG_CHECKPOINT_RESTORE config option?


--
Best regards,
Stanislav Kinsbursky
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