apparmor: fix ptrace label match when matching stacked labels

Given a label with a profile stack of
  A//&B or A//&C ...

A ptrace rule should be able to specify a generic trace pattern with
a rule like

  ptrace trace A//&**,

however this is failing because while the correct label match routine
is called, it is being done post label decomposition so it is always
being done against a profile instead of the stacked label.

To fix this refactor the cross check to pass the full peer label in to
the label_match.

Fixes: 290f458a4f16 ("apparmor: allow ptrace checks to be finer grained than just capability")
Cc: Stable <stable@vger.kernel.org>
Reported-by: Matthew Garrett <mjg59@google.com>
Tested-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/include/perms.h

@@ -133,6 +133,9 @@ extern struct aa_perms allperms;
 #define xcheck_labels_profiles(L1, L2, FN, args...)		\
 	xcheck_ns_labels((L1), (L2), xcheck_ns_profile_label, (FN), args)
 
+#define xcheck_labels(L1, L2, P, FN1, FN2)			\
+	xcheck(fn_for_each((L1), (P), (FN1)), fn_for_each((L2), (P), (FN2)))
+
 
 void aa_perm_mask_to_str(char *str, const char *chrs, u32 mask);
 void aa_audit_perm_names(struct audit_buffer *ab, const char **names, u32 mask);

security/apparmor/ipc.c

@@ -64,40 +64,48 @@ static void audit_ptrace_cb(struct audit_buffer *ab, void *va)
 			FLAGS_NONE, GFP_ATOMIC);
 }
 
+/* assumes check for PROFILE_MEDIATES is already done */
 /* TODO: conditionals */
 static int profile_ptrace_perm(struct aa_profile *profile,
-			       struct aa_profile *peer, u32 request,
-			       struct common_audit_data *sa)
+			     struct aa_label *peer, u32 request,
+			     struct common_audit_data *sa)
 {
 	struct aa_perms perms = { };
 
-	/* need because of peer in cross check */
-	if (profile_unconfined(profile) ||
-	    !PROFILE_MEDIATES(profile, AA_CLASS_PTRACE))
-		return 0;
-
-	aad(sa)->peer = &peer->label;
-	aa_profile_match_label(profile, &peer->label, AA_CLASS_PTRACE, request,
+	aad(sa)->peer = peer;
+	aa_profile_match_label(profile, peer, AA_CLASS_PTRACE, request,
 			       &perms);
 	aa_apply_modes_to_perms(profile, &perms);
 	return aa_check_perms(profile, &perms, request, sa, audit_ptrace_cb);
 }
 
-static int cross_ptrace_perm(struct aa_profile *tracer,
-			     struct aa_profile *tracee, u32 request,
-			     struct common_audit_data *sa)
+static int profile_tracee_perm(struct aa_profile *tracee,
+			       struct aa_label *tracer, u32 request,
+			       struct common_audit_data *sa)
 {
+	if (profile_unconfined(tracee) || unconfined(tracer) ||
+	    !PROFILE_MEDIATES(tracee, AA_CLASS_PTRACE))
+		return 0;
+
+	return profile_ptrace_perm(tracee, tracer, request, sa);
+}
+
+static int profile_tracer_perm(struct aa_profile *tracer,
+			       struct aa_label *tracee, u32 request,
+			       struct common_audit_data *sa)
+{
+	if (profile_unconfined(tracer))
+		return 0;
+
 	if (PROFILE_MEDIATES(tracer, AA_CLASS_PTRACE))
-		return xcheck(profile_ptrace_perm(tracer, tracee, request, sa),
-			      profile_ptrace_perm(tracee, tracer,
-						  request << PTRACE_PERM_SHIFT,
-						  sa));
-	/* policy uses the old style capability check for ptrace */
-	if (profile_unconfined(tracer) || tracer == tracee)
+		return profile_ptrace_perm(tracer, tracee, request, sa);
+
+	/* profile uses the old style capability check for ptrace */
+	if (&tracer->label == tracee)
 		return 0;
 
 	aad(sa)->label = &tracer->label;
-	aad(sa)->peer = &tracee->label;
+	aad(sa)->peer = tracee;
 	aad(sa)->request = 0;
 	aad(sa)->error = aa_capable(&tracer->label, CAP_SYS_PTRACE, 1);
 
@@ -115,10 +123,13 @@ static int cross_ptrace_perm(struct aa_profile *tracer,
 int aa_may_ptrace(struct aa_label *tracer, struct aa_label *tracee,
 		  u32 request)
 {
+	struct aa_profile *profile;
+	u32 xrequest = request << PTRACE_PERM_SHIFT;
 	DEFINE_AUDIT_DATA(sa, LSM_AUDIT_DATA_NONE, OP_PTRACE);
 
-	return xcheck_labels_profiles(tracer, tracee, cross_ptrace_perm,
-				      request, &sa);
+	return xcheck_labels(tracer, tracee, profile,
+			profile_tracer_perm(profile, tracee, request, &sa),
+			profile_tracee_perm(profile, tracer, xrequest, &sa));
 }