[PATCH] selinux: check level category sets once at load time

As reported by Jiri Vozar, commit 7edea6e8c8e8 ("selinux: beef up
isvalid checks") introduces a new loop in mls_level_isvalid() that
causes ~89-94% throughput regression in System V IPC message queue
operations (msgsnd/msgrcv).

Move the expensive part of the ebitmap checking to policy load time
instead as the reporter suggested.

Reported-by: Jiri Vozar <[email protected]>
Link: https://lore.kernel.org/selinux/CAMgFczCi2Z011dNf84Amc0Q-qnTt0+VUjWY+Y7zPyXdaH35Jvw@mail.gmail.com/
Fixes: 7edea6e8c8e8 ("selinux: beef up isvalid checks")
Suggested-by: Jiri Vozar <[email protected]>
Signed-off-by: Stephen Smalley <[email protected]>
---
 security/selinux/ss/mls.c      | 24 +++++++-----------------
 security/selinux/ss/policydb.c | 23 +++++++++++++++++++++++
 2 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/security/selinux/ss/mls.c b/security/selinux/ss/mls.c
index 3cd36e2015fa..40c62600650e 100644
--- a/security/selinux/ss/mls.c
+++ b/security/selinux/ss/mls.c
@@ -160,9 +160,6 @@ bool mls_level_isvalid(const struct policydb *p, const struct mls_level *l)
 {
 	const char *name;
 	const struct level_datum *levdatum;
-	struct ebitmap_node *node;
-	u32 bit;
-	int rc;
 
 	if (!l->sens || l->sens > p->p_levels.nprim)
 		return false;
@@ -176,21 +173,14 @@ bool mls_level_isvalid(const struct policydb *p, const struct mls_level *l)
 		return false;
 
 	/*
-	 * Validate that all bits set in l->cat are also be set in
-	 * levdatum->level->cat and no bit in l->cat is larger than
-	 * p->p_cats.nprim.
+	 * l is valid iff every bit in l->cat is set in levdatum->level.cat
+	 * and no bit in l->cat is larger than p->p_cats.nprim.
+	 * policydb_index() has already verified that every bit set in
+	 * levdatum->level.cat names a defined category, so containment is
+	 * sufficient here.
 	 */
-	rc = ebitmap_contains(&levdatum->level.cat, &l->cat,
-			      p->p_cats.nprim);
-	if (!rc)
-		return false;
-
-	ebitmap_for_each_positive_bit(&levdatum->level.cat, node, bit) {
-		if (!sym_name(p, SYM_CATS, bit))
-			return false;
-	}
-
-	return true;
+	return ebitmap_contains(&levdatum->level.cat, &l->cat,
+				p->p_cats.nprim);
 }
 
 bool mls_range_isvalid(const struct policydb *p, const struct mls_range *r)
diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
index f141f007d96d..b75c977c6673 100644
--- a/security/selinux/ss/policydb.c
+++ b/security/selinux/ss/policydb.c
@@ -670,6 +670,23 @@ static int cat_index(void *key, void *datum, void *datap)
 	return 0;
 }
 
+static int sens_cat_index_check(void *key, void *datum, void *datap)
+{
+	struct policydb *p = datap;
+	struct level_datum *levdatum = datum;
+	struct ebitmap_node *node;
+	u32 bit;
+
+	ebitmap_for_each_positive_bit(&levdatum->level.cat, node, bit) {
+		if (bit >= p->p_cats.nprim || !sym_name(p, SYM_CATS, bit)) {
+			pr_err("SELinux: sensitivity %s allows undefined category %u\n",
+				(const char *)key, bit + 1);
+			return -EINVAL;
+		}
+	}
+	return 0;
+}
+
 /* clang-format off */
 static int (*const index_f[SYM_NUM])(void *key, void *datum, void *datap) = {
 	common_index,
@@ -793,6 +810,12 @@ static int policydb_index(struct policydb *p)
 		}
 	}
 
+	if (p->mls_enabled) {
+		rc = hashtab_map(&p->p_levels.table, sens_cat_index_check, p);
+		if (rc)
+			goto out;
+	}
+
 	rc = 0;
 out:
 	return rc;
-- 
2.55.0