Reapply: "Handle unmount for isolated process correctly (tiann#2696)"

Isolated processes can be directly forked from zygote, but current code
doesn't handle it well. Fix it by unmounting unconditionally if isolated
process is forked from zygote.

Author: aviraxp

kernel/core_hook.c

@@ -62,7 +62,7 @@ static inline bool is_allow_su()
 	return ksu_is_allow_uid(current_uid().val);
 }
 
-static inline bool is_unsupported_uid(uid_t uid)
+static inline bool is_unsupported_app_uid(uid_t uid)
 {
 #define LAST_APPLICATION_UID 19999
 	uid_t appid = uid % 100000;
@@ -468,14 +468,13 @@ int ksu_handle_prctl(int option, unsigned long arg2, unsigned long arg3,
 	return 0;
 }
 
-static bool is_appuid(kuid_t uid)
+static bool is_non_appuid(kuid_t uid)
 {
 #define PER_USER_RANGE 100000
 #define FIRST_APPLICATION_UID 10000
-#define LAST_APPLICATION_UID 19999
 
 	uid_t appid = uid.val % PER_USER_RANGE;
-	return appid >= FIRST_APPLICATION_UID && appid <= LAST_APPLICATION_UID;
+	return appid < FIRST_APPLICATION_UID;
 }
 
 static bool should_umount(struct path *path)
@@ -547,13 +546,25 @@ int ksu_handle_setuid(struct cred *new, const struct cred *old)
 		return 0;
 	}
 
-	if (!is_appuid(new_uid) || is_unsupported_uid(new_uid.val)) {
-		// pr_info("handle setuid ignore non application or isolated uid: %d\n", new_uid.val);
+	if (is_non_appuid(new_uid)) {
+#ifdef CONFIG_KSU_DEBUG
+		pr_info("handle setuid ignore non application uid: %d\n", new_uid.val);
+#endif
 		return 0;
 	}
 
+	// isolated process may be directly forked from zygote, always unmount
+	if (is_unsupported_app_uid(new_uid.val)) {
+#ifdef CONFIG_KSU_DEBUG
+		pr_info("handle umount for unsupported application uid: %d\n", new_uid.val);
+#endif
+		goto do_umount;
+	}
+
 	if (ksu_is_allow_uid(new_uid.val)) {
-		// pr_info("handle setuid ignore allowed application: %d\n", new_uid.val);
+#ifdef CONFIG_KSU_DEBUG
+		pr_info("handle setuid ignore allowed application: %d\n", new_uid.val);
+#endif
 		return 0;
 	}
 
@@ -565,11 +576,11 @@ int ksu_handle_setuid(struct cred *new, const struct cred *old)
 #endif
 	}
 
+do_umount:
 	// check old process's selinux context, if it is not zygote, ignore it!
 	// because some su apps may setuid to untrusted_app but they are in global mount namespace
 	// when we umount for such process, that is a disaster!
-	bool is_zygote_child = is_zygote(old->security);
-	if (!is_zygote_child) {
+	if (!is_zygote(old->security)) {
 		pr_info("handle umount ignore non zygote child: %d\n",
 			current->pid);
 		return 0;