Stephen Smalley wrote:
On Wed, 2007-12-19 at 11:15 -0500, Stephen Smalley wrote:
On Wed, 2007-12-19 at 11:09 +1100, James Morris wrote:
On Tue, 18 Dec 2007, Eamon Walsh wrote:
Stephen Smalley wrote:
If a (buggy) caller passes a requested permission value of zero to
avc_has_perm, it correctly returns a permission denial (if enforcing),
Now I'm questioning why we don't just return success. Doesn't everyone have
permission to do nothing? It seems odd to think that a process could receive
"granted" for a set of permissions A, but "denied" for a subset of A.
Given that the caller is buggy, we don't really know what it's trying to
do, so denying access seems prudent.
Can we get the audit log to produce something unparseable by audit2allow,
as we don't _want_ policy being generated in response to a buggy caller ?
At present, it generates no avc message in permissive (avc_audit entered
with requested == 0 and result == 0) and a misleading avc message in
enforcing (avc_audit entered with requested == 0 and result < 0),
neither of which will generate any policy.
If we change it to consistently generate an:
avc: denied null for scontext=...
then audit2allow would try to create an allow rule like:
allow a_t b_t:class null;
which would compile but fail when one tries to insert the module, since
null is not a defined permission in the base policy.
I don't think we want to generate an unparseable avc message, whatever
that might mean, as that too could potentially break audit2allow and in
a less understandable way, and we want these failures to be noticeable,
just not immediately fatal to the system (ala BUG_ON or assert).
Oh, the other reason to keep it in the existing format is to ensure that
setroubleshoot picks up on it, since users are now trained to look for
its alerts rather than inspecting the audit log for SELinux denials.
How about the following:
Index: libselinux/src/avc.c
===================================================================
--- libselinux/src/avc.c (revision 2708)
+++ libselinux/src/avc.c (working copy)
@@ -756,12 +756,19 @@
denied = requested & ~avd->allowed;
if (denied) {
+ /* Permissions were denied */
audited = denied;
if (!(audited & avd->auditdeny))
return;
+ } else if (!requested) {
+ /* Request was made with "null" permission vector */
+ audited = requested;
+ denied = 1;
} else if (result) {
+ /* Another error besides a denial occurred */
audited = denied = requested;
} else {
+ /* Permissions were granted */
audited = requested;
if (!(audited & avd->auditallow))
return;
--
Eamon Walsh <ewalsh@xxxxxxxxxxxxx>
National Security Agency
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