apparmor: compute xmatch permissions on profile load

Rather than computing xmatch permissions each time access is requested,
these permissions can be computed once on profile load and stored for
lookup.
Signed-off-by: Mike Salvatore <mike.salvatore@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/domain.c

@@ -339,7 +339,7 @@ static int aa_xattrs_match(const struct linux_binprm *bprm,
 			/* Check xattr value */
 			state = aa_dfa_match_len(profile->xmatch, state, value,
 						 size);
-			perm = dfa_user_allow(profile->xmatch, state);
+			perm = profile->xmatch_perms[state];
 			if (!(perm & MAY_EXEC)) {
 				ret = -EINVAL;
 				goto out;
@@ -419,7 +419,7 @@ static struct aa_label *find_attach(const struct linux_binprm *bprm,
 
 			state = aa_dfa_leftmatch(profile->xmatch, DFA_START,
 						 name, &count);
-			perm = dfa_user_allow(profile->xmatch, state);
+			perm = profile->xmatch_perms[state];
 			/* any accepting state means a valid match. */
 			if (perm & MAY_EXEC) {
 				int ret = 0;

security/apparmor/include/policy.h

@@ -104,6 +104,7 @@ struct aa_data {
  * @attach: human readable attachment string
  * @xmatch: optional extended matching for unconfined executables names
  * @xmatch_len: xmatch prefix len, used to determine xmatch priority
+ * @xmatch_perms: precomputed permissions for the xmatch DFA indexed by state
  * @audit: the auditing mode of the profile
  * @mode: the enforcement mode of the profile
  * @path_flags: flags controlling path generation behavior
@@ -140,6 +141,7 @@ struct aa_profile {
 	const char *attach;
 	struct aa_dfa *xmatch;
 	unsigned int xmatch_len;
+	u32 *xmatch_perms;
 	enum audit_mode audit;
 	long mode;
 	u32 path_flags;

security/apparmor/policy.c

@@ -231,6 +231,7 @@ void aa_free_profile(struct aa_profile *profile)
 	kfree_sensitive(profile->secmark);
 	kfree_sensitive(profile->dirname);
 	aa_put_dfa(profile->xmatch);
+	kvfree(profile->xmatch_perms);
 	aa_put_dfa(profile->policy.dfa);
 
 	if (profile->data) {

security/apparmor/policy_unpack.c

@@ -669,6 +669,23 @@ static int datacmp(struct rhashtable_compare_arg *arg, const void *obj)
 	return strcmp(data->key, *key);
 }
 
+static u32 *aa_compute_xmatch_perms(struct aa_dfa *xmatch)
+{
+	u32 *perms_table;
+	int state;
+	int state_count = xmatch->tables[YYTD_ID_BASE]->td_lolen;
+
+	// DFAs are restricted from having a state_count of less than 2
+	perms_table = kvcalloc(state_count, sizeof(u32), GFP_KERNEL);
+
+	// Since perms_table is initialized with zeroes via kvcalloc(), we can
+	// skip the trap state (state == 0)
+	for (state = 1; state < state_count; state++)
+		perms_table[state] = dfa_user_allow(xmatch, state);
+
+	return perms_table;
+}
+
 /**
  * unpack_profile - unpack a serialized profile
  * @e: serialized data extent information (NOT NULL)
@@ -727,13 +744,16 @@ static struct aa_profile *unpack_profile(struct aa_ext *e, char **ns_name)
 		info = "bad xmatch";
 		goto fail;
 	}
-	/* xmatch_len is not optional if xmatch is set */
+	/* neither xmatch_len not xmatch_perms are optional if xmatch is set */
 	if (profile->xmatch) {
 		if (!unpack_u32(e, &tmp, NULL)) {
 			info = "missing xmatch len";
 			goto fail;
 		}
 		profile->xmatch_len = tmp;
+
+		profile->xmatch_perms = aa_compute_xmatch_perms(
+			profile->xmatch);
 	}
 
 	/* disconnected attachment string is optional */