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Re: IPC auditing (Was: Re: Another slab size-32 leak 2.6.16-rc4-mm2)



On Tuesday 28 February 2006 16:01, Stephen Smalley wrote:
> On Tue, 2006-02-28 at 15:20 +0100, Stephan Mueller wrote:
> > [...]
> >
> > error_path:
> >        kfree(ctx);
> >        audit_panic("error in audit_ipc_context");
> >
> > You free ctx although it has not been allocated - I do not like that ;-)
>
> Common convention is to initialize ctx to NULL upon declaration, and
> then such kfree() calls are safe on the error path.

uh, I see. Nevermind :-)
>
> > Please tell me if I misunderstand anything: The question for you
> > is whether to keep this function. This function is about to collect
> > labels for IPC functions. If this function is gone, you cannot audit any
> > labels for the IPC functions any more?!
>
> IIUC, they are asking about which IPC functions/operations require
> collection of the labels, not whether the labels should be audited at
> all.  At present, audit_ipc_context is being called indirectly via
> audit_ipc_perms from various IPC_SET operations and directly from
> ipcperms() (but the latter is being proposed for removal).  I think that
> there is some confusion here because in the CAPP case, the basic syscall
> auditing provides much of the required information and you therefore
> don't need additional hooks except in the IPC_SET case?  Whereas in the
> LSPP case we need to always be collecting the label information?

Indeed, the LSPP audit always needs the labels of the involved parties: 
subjects and objects. There is no exception to this rule.
>
> > If this is the case, then this function needs to stay, because:
> >
> > - syscalls msg*, sem*, shm* (except shmdt) do DAC checks - now, they also
> > perform MAC checks by calling appropriate SELinux hooks (as required by
> > the ST as IPC mechanisms are subject to MAC - I think shmdt now must also
> > be subject to MAC at least), then these syscalls must perform audit
>
> shmdt merely detaches a previously attached segment from the address
> space of the calling process - there is nothing new to check there, and
> the real work is all deferred anyway until the close method is called.
> If the process was authorized to shmat() the object in the first place,
> then it should be allowed to shmdt() it from its own address space.

I was not sure of that for shmdt - but based on your description, no audit 
would be required.
>
> > - the audit requirement for IPC calls is specified in FAU_GEN.1.1 LSPP in
> > the table: "All decisions on requests for information flow" must be
> > audited
> >
> > - FAU_SAR.3 LSPP requires that subject and object sensitivity labels are
> > to be audited.
> >
> > Ergo, the functionality in question must stay.
>
> It sounds like the functionality should actually be expanded based on
> the above.  Possibly even calling audit_ipc_context() from the SELinux
> hooks themselves to capture all cases.

Sorry, I cannot comment on that as I am a bit unfamiliar with SELinux atm. But 
as said above: subjects and objects must be listed in the audit trail at any 
case (as long as there is a corresponding object and/or subject).

Ciao
Stephan


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