Unmount isolated process which forks from zygote unconditionally (tiann/KernelSU#2747)

Rethink about this patch, isolated process which directly forks from
zygote is just like normal app, so there is no reason apps won't crash
but Isolated process will. Also zygote reopens fd before actually fork,
so it should be fine.

This reverts commit tiann/KernelSU@2a1741d.

Author: aviraxp

kernel/core_hook.c

@@ -64,7 +64,7 @@ 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;
@@ -592,14 +592,13 @@ 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)
@@ -676,13 +675,25 @@ 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 or isolated 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;
 	}
 
@@ -694,11 +705,11 @@ 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;