From 19182ffddf6f7c87bacab4b9f91cfaec3ee79537 Mon Sep 17 00:00:00 2001
From: LoveSy <shana@zju.edu.cn>
Date: Wed, 29 Dec 2021 07:16:20 +0800
Subject: [PATCH] If dt fstab contains error, fallback to default fstab

See https://cs.android.com/android/platform/superproject/+/master:system/core/init/first_stage_mount.cpp;drc=master;l=155

From the source of `FirstStageMount`, dt fstab can fail gracefully and
if any error occurs it will fall back to default fstab. Magisk now
replaces the default fstab and dt fstab unconditionally, bringing potential
errors to the default fstab and causing init fails to load partitions.
---
 native/jni/init/twostage.cpp | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/native/jni/init/twostage.cpp b/native/jni/init/twostage.cpp
index bb878ef08..132250672 100644
--- a/native/jni/init/twostage.cpp
+++ b/native/jni/init/twostage.cpp
@@ -27,7 +27,11 @@ void fstab_entry::to_file(FILE *fp) {
 line[val##1] = '\0'; \
 entry.val = &line[val##0];
 
-static void read_fstab_file(const char *fstab_file, vector<fstab_entry> &fstab) {
+static bool read_fstab_file(const char *fstab_file, vector<fstab_entry> &fstab) {
+    if (!fstab_file || fstab_file[0] == '\0') {
+        LOGE("fstab file is empty");
+        return false;
+    }
     file_readline(fstab_file, [&](string_view l) -> bool {
         if (l[0] == '#' || l.length() == 1)
             return true;
@@ -51,6 +55,7 @@ static void read_fstab_file(const char *fstab_file, vector<fstab_entry> &fstab)
         fstab.emplace_back(move(entry));
         return true;
     });
+    return true;
 }
 
 #define FSR "/first_stage_ramdisk"
@@ -101,6 +106,7 @@ exit_loop:
 
     if (!fstab.empty()) {
         // Dump dt fstab to fstab file in rootfs and force init to use it instead
+        bool should_skip = false; // If there's any error in dt fstab and if so, skip loading it
 
         // All dt fstab entries should be first_stage_mount
         for (auto &entry : fstab) {
@@ -109,6 +115,10 @@ exit_loop:
                     entry.fsmgr_flags += ',';
                 entry.fsmgr_flags += "first_stage_mount";
             }
+            // If the entry contains slotselect but the current slot is empty, error occurs
+            if (config->slot[0] == '\0' && str_contains(entry.fsmgr_flags, "slotselect")) {
+                should_skip = true;
+            } // TODO: else if expected_field checks and fs_mgr_flags checks
         }
 
         if (fstab_file[0] == '\0') {
@@ -122,18 +132,18 @@ exit_loop:
             }
             sprintf(fstab_file, "fstab.%s", suffix);
         }
+        if (should_skip) {
+            // When dt fstab fails, fall back to default fstab
+            LOGI("dt fstab contains error, falling back to default fstab");
+            fstab.clear();
+            if (!read_fstab_file(fstab_file, fstab)) return;
 
-        // Patch init to force IsDtFstabCompatible() return false
-        auto init = mmap_data("/init", true);
-        init.patch({ make_pair("android,fstab", "xxx") });
-    } else {
-        if (fstab_file[0] == '\0') {
-            LOGE("Cannot find fstab");
-            return;
+        } else {
+            // Patch init to force IsDtFstabCompatible() return false
+            auto init = mmap_data("/init", true);
+            init.patch({make_pair("android,fstab", "xxx")});
         }
-        // Parse and load the fstab file
-        read_fstab_file(fstab_file, fstab);
-    }
+    } else if (!read_fstab_file(fstab_file, fstab)) return;
 
     // Append oppo's custom fstab
     if (access("oplus.fstab", F_OK) == 0) {