tomoyo: ignore data race while checking quota

syzbot is reporting that tomoyo's quota check is racy [1]. But this check
is tolerant of some degree of inaccuracy. Thus, teach KCSAN to ignore
this data race.

[1] https://syzkaller.appspot.com/bug?id=999533deec7ba6337f8aa25d8bd1a4d5f7e50476Reported-by: Nsyzbot <syzbot+0789a72b46fd91431bd8@syzkaller.appspotmail.com>
Signed-off-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

security/tomoyo/file.c

@@ -362,14 +362,14 @@ static bool tomoyo_merge_path_acl(struct tomoyo_acl_info *a,
 {
 	u16 * const a_perm = &container_of(a, struct tomoyo_path_acl, head)
 		->perm;
-	u16 perm = *a_perm;
+	u16 perm = READ_ONCE(*a_perm);
 	const u16 b_perm = container_of(b, struct tomoyo_path_acl, head)->perm;
 
 	if (is_delete)
 		perm &= ~b_perm;
 	else
 		perm |= b_perm;
-	*a_perm = perm;
+	WRITE_ONCE(*a_perm, perm);
 	return !perm;
 }
 
@@ -437,7 +437,7 @@ static bool tomoyo_merge_mkdev_acl(struct tomoyo_acl_info *a,
 {
 	u8 *const a_perm = &container_of(a, struct tomoyo_mkdev_acl,
 					 head)->perm;
-	u8 perm = *a_perm;
+	u8 perm = READ_ONCE(*a_perm);
 	const u8 b_perm = container_of(b, struct tomoyo_mkdev_acl, head)
 		->perm;
 
@@ -445,7 +445,7 @@ static bool tomoyo_merge_mkdev_acl(struct tomoyo_acl_info *a,
 		perm &= ~b_perm;
 	else
 		perm |= b_perm;
-	*a_perm = perm;
+	WRITE_ONCE(*a_perm, perm);
 	return !perm;
 }
 
@@ -517,14 +517,14 @@ static bool tomoyo_merge_path2_acl(struct tomoyo_acl_info *a,
 {
 	u8 * const a_perm = &container_of(a, struct tomoyo_path2_acl, head)
 		->perm;
-	u8 perm = *a_perm;
+	u8 perm = READ_ONCE(*a_perm);
 	const u8 b_perm = container_of(b, struct tomoyo_path2_acl, head)->perm;
 
 	if (is_delete)
 		perm &= ~b_perm;
 	else
 		perm |= b_perm;
-	*a_perm = perm;
+	WRITE_ONCE(*a_perm, perm);
 	return !perm;
 }
 
@@ -655,7 +655,7 @@ static bool tomoyo_merge_path_number_acl(struct tomoyo_acl_info *a,
 {
 	u8 * const a_perm = &container_of(a, struct tomoyo_path_number_acl,
 					  head)->perm;
-	u8 perm = *a_perm;
+	u8 perm = READ_ONCE(*a_perm);
 	const u8 b_perm = container_of(b, struct tomoyo_path_number_acl, head)
 		->perm;
 
@@ -663,7 +663,7 @@ static bool tomoyo_merge_path_number_acl(struct tomoyo_acl_info *a,
 		perm &= ~b_perm;
 	else
 		perm |= b_perm;
-	*a_perm = perm;
+	WRITE_ONCE(*a_perm, perm);
 	return !perm;
 }
 

security/tomoyo/network.c

@@ -233,14 +233,14 @@ static bool tomoyo_merge_inet_acl(struct tomoyo_acl_info *a,
 {
 	u8 * const a_perm =
 		&container_of(a, struct tomoyo_inet_acl, head)->perm;
-	u8 perm = *a_perm;
+	u8 perm = READ_ONCE(*a_perm);
 	const u8 b_perm = container_of(b, struct tomoyo_inet_acl, head)->perm;
 
 	if (is_delete)
 		perm &= ~b_perm;
 	else
 		perm |= b_perm;
-	*a_perm = perm;
+	WRITE_ONCE(*a_perm, perm);
 	return !perm;
 }
 
@@ -259,14 +259,14 @@ static bool tomoyo_merge_unix_acl(struct tomoyo_acl_info *a,
 {
 	u8 * const a_perm =
 		&container_of(a, struct tomoyo_unix_acl, head)->perm;
-	u8 perm = *a_perm;
+	u8 perm = READ_ONCE(*a_perm);
 	const u8 b_perm = container_of(b, struct tomoyo_unix_acl, head)->perm;
 
 	if (is_delete)
 		perm &= ~b_perm;
 	else
 		perm |= b_perm;
-	*a_perm = perm;
+	WRITE_ONCE(*a_perm, perm);
 	return !perm;
 }
 

security/tomoyo/util.c

@@ -1058,30 +1058,30 @@ bool tomoyo_domain_quota_is_ok(struct tomoyo_request_info *r)
 
 		if (ptr->is_deleted)
 			continue;
+		/*
+		 * Reading perm bitmap might race with tomoyo_merge_*() because
+		 * caller does not hold tomoyo_policy_lock mutex. But exceeding
+		 * max_learning_entry parameter by a few entries does not harm.
+		 */
 		switch (ptr->type) {
 		case TOMOYO_TYPE_PATH_ACL:
-			perm = container_of(ptr, struct tomoyo_path_acl, head)
-				->perm;
+			data_race(perm = container_of(ptr, struct tomoyo_path_acl, head)->perm);
 			break;
 		case TOMOYO_TYPE_PATH2_ACL:
-			perm = container_of(ptr, struct tomoyo_path2_acl, head)
-				->perm;
+			data_race(perm = container_of(ptr, struct tomoyo_path2_acl, head)->perm);
 			break;
 		case TOMOYO_TYPE_PATH_NUMBER_ACL:
-			perm = container_of(ptr, struct tomoyo_path_number_acl,
-					    head)->perm;
+			data_race(perm = container_of(ptr, struct tomoyo_path_number_acl, head)
+				  ->perm);
 			break;
 		case TOMOYO_TYPE_MKDEV_ACL:
-			perm = container_of(ptr, struct tomoyo_mkdev_acl,
-					    head)->perm;
+			data_race(perm = container_of(ptr, struct tomoyo_mkdev_acl, head)->perm);
 			break;
 		case TOMOYO_TYPE_INET_ACL:
-			perm = container_of(ptr, struct tomoyo_inet_acl,
-					    head)->perm;
+			data_race(perm = container_of(ptr, struct tomoyo_inet_acl, head)->perm);
 			break;
 		case TOMOYO_TYPE_UNIX_ACL:
-			perm = container_of(ptr, struct tomoyo_unix_acl,
-					    head)->perm;
+			data_race(perm = container_of(ptr, struct tomoyo_unix_acl, head)->perm);
 			break;
 		case TOMOYO_TYPE_MANUAL_TASK_ACL:
 			perm = 0;