[PATCH][SRU][disco] UBUNTU: SAUCE: apparmor: fix nnp subset test for unconfined

[John Johansen]

The subset test is not taking into account the unconfined exception
which will cause profile transitions in the stacked confinement
case to fail when no_new_privs is applied.

This fixes a regression introduced in the 4.17 kernel caused by the
reworking of domain transitions.

Fixes: 9fcf78cca1986 ("apparmor: update domain transitions that are subsets of confinement at nnp")
BugLink: https://bugs.launchpad.net/bugs/1844186
Signed-off-by: John Johansen <john.johansen at canonical.com>
---
 security/apparmor/domain.c        |  8 ++++----
 security/apparmor/include/label.h |  1 +
 security/apparmor/label.c         | 33 +++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
index 3b266a438776..1c3cd1228e97 100644
--- a/security/apparmor/domain.c
+++ b/security/apparmor/domain.c
@@ -935,7 +935,7 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm)
 	 * aways results in a further reduction of permissions.
 	 */
 	if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) &&
-	    !unconfined(label) && !aa_label_is_subset(new, ctx->nnp)) {
+	    !unconfined(label) && !aa_label_is_unconfined_subset(new, ctx->nnp)) {
 		error = -EPERM;
 		info = "no new privs";
 		goto audit;
@@ -1213,7 +1213,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
 		 * reduce restrictions.
 		 */
 		if (task_no_new_privs(current) && !unconfined(label) &&
-		    !aa_label_is_subset(new, ctx->nnp)) {
+		    !aa_label_is_unconfined_subset(new, ctx->nnp)) {
 			/* not an apparmor denial per se, so don't log it */
 			AA_DEBUG("no_new_privs - change_hat denied");
 			error = -EPERM;
@@ -1234,7 +1234,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
 		 * reduce restrictions.
 		 */
 		if (task_no_new_privs(current) && !unconfined(label) &&
-		    !aa_label_is_subset(previous, ctx->nnp)) {
+		    !aa_label_is_unconfined_subset(previous, ctx->nnp)) {
 			/* not an apparmor denial per se, so don't log it */
 			AA_DEBUG("no_new_privs - change_hat denied");
 			error = -EPERM;
@@ -1430,7 +1430,7 @@ int aa_change_profile(const char *fqname, int flags)
 		 * reduce restrictions.
 		 */
 		if (task_no_new_privs(current) && !unconfined(label) &&
-		    !aa_label_is_subset(new, ctx->nnp)) {
+		    !aa_label_is_unconfined_subset(new, ctx->nnp)) {
 			/* not an apparmor denial per se, so don't log it */
 			AA_DEBUG("no_new_privs - change_hat denied");
 			error = -EPERM;
diff --git a/security/apparmor/include/label.h b/security/apparmor/include/label.h
index d871e7ff0952..71af9f6f58ed 100644
--- a/security/apparmor/include/label.h
+++ b/security/apparmor/include/label.h
@@ -285,6 +285,7 @@ bool aa_label_init(struct aa_label *label, int size);
 struct aa_label *aa_label_alloc(int size, struct aa_proxy *proxy, gfp_t gfp);
 
 bool aa_label_is_subset(struct aa_label *set, struct aa_label *sub);
+bool aa_label_is_unconfined_subset(struct aa_label *set, struct aa_label *sub);
 struct aa_profile *__aa_label_next_not_in_set(struct label_it *I,
 					     struct aa_label *set,
 					     struct aa_label *sub);
diff --git a/security/apparmor/label.c b/security/apparmor/label.c
index 83e4f6d62c66..8de6f1655bb1 100644
--- a/security/apparmor/label.c
+++ b/security/apparmor/label.c
@@ -555,6 +555,39 @@ bool aa_label_is_subset(struct aa_label *set, struct aa_label *sub)
 	return __aa_label_next_not_in_set(&i, set, sub) == NULL;
 }
 
+/**
+ * aa_label_is_unconfined_subset - test if @sub is a subset of @set
+ * @set: label to test against
+ * @sub: label to test if is subset of @set
+ *
+ * This checks for subset but taking into account unconfined. IF
+ * @sub contains an unconfined profile that does not have a matching
+ * unconfined in @set then this will not cause the test to fail.
+ * Conversely we don't care about an unconfined in @set that is not in
+ * @sub
+ *
+ * Returns: true if @sub is special_subset of @set
+ *     else false
+ */
+bool aa_label_is_unconfined_subset(struct aa_label *set, struct aa_label *sub)
+{
+	struct label_it i = { };
+	struct aa_profile *p;
+
+	AA_BUG(!set);
+	AA_BUG(!sub);
+
+	if (sub == set)
+		return true;
+
+	do {
+		p = __aa_label_next_not_in_set(&i, set, sub);
+		if (p && !profile_unconfined(p))
+			break;
+	} while (p);
+
+	return p == NULL;
+}
 
 
 /**
-- 
2.17.1