Respect default errors value on EXT FS

module/jni/include/utils.hpp

@@ -4,6 +4,7 @@
 #include <functional>
 #include "logging.hpp"
 #include "zygisk.hpp"
+#include "mountinfo_parser.hpp"
 
 #define DCL_HOOK_FUNC(ret, func, ...)         \
     ret (*old_##func)(__VA_ARGS__) = nullptr; \
@@ -36,4 +37,5 @@ namespace Utils
     int isUserAppUID(int uid);
     bool hookPLTByName(zygisk::Api *api, const std::string &libName, const std::string &symbolName, void *hookFunc, void **origFunc);
     int forkAndInvoke(const std::function<int()> &lambda);
+    const char *getExtErrorsBehavior(const Parsers::mountinfo_entry &entry);
 }

module/jni/modules.cpp

@@ -93,28 +93,26 @@ void doRemount()
         if (mount.getMountPoint() == "/data")
         {
             const auto &superOptions = mount.getSuperOptions();
+            if (!superOptions.contains("errors"))
+                break;
+
+            // Remount /data only if errors behavior is not the same as superblock's
+            const char *sb_errors = Utils::getExtErrorsBehavior(mount);
+            if (!sb_errors || superOptions.at("errors") == sb_errors)
+                break;
+
             const auto &mountOptions = mount.getMountOptions();
-
+            unsigned long flags = MS_REMOUNT;
-            // If errors=remount-ro, remount it with errors=continue
+            for (const auto &flagName : mount_flags_procfs)
-            if (superOptions.contains("errors") && superOptions.at("errors") == "remount-ro")
             {
-                unsigned long flags = MS_REMOUNT;
+                if (mountOptions.contains(flagName.first))
-                for (const auto &flagName : mount_flags_procfs)
+                    flags |= flagName.second;
-                {
-                    if (mountOptions.contains(flagName.first))
-                        flags |= flagName.second;
-                }
-
-                if (::mount(NULL, "/data", NULL, flags, "errors=continue") == 0)
-                {
-                    LOGD("mount(NULL, \"/data\", NULL, 0x%lx, \"errors=continue\") returned 0", flags);
-                }
-                else
-                {
-                    LOGW("mount(NULL, \"/data\", NULL, 0x%lx, \"errors=continue\") returned -1: %d (%s)", flags, errno, strerror(errno));
-                }
             }
 
+            if (::mount(NULL, "/data", NULL, flags, (std::string("errors=") + sb_errors).c_str()) == 0)
+                LOGD("mount(NULL, \"/data\", NULL, 0x%lx, ...) returned 0", flags);
+            else
+                LOGW("mount(NULL, \"/data\", NULL, 0x%lx, ...) returned -1: %d (%s)", flags, errno, strerror(errno));
             break;
         }
     }

module/jni/utils.cpp

@@ -1,11 +1,13 @@
+#include <fstream>
 #include <string.h>
+#include <cstdint>
 #include <string>
 #include <functional>
-#include <format>
 #include <unistd.h>
 #include <sys/wait.h>
 #include <sched.h>
 #include <fcntl.h>
+#include <endian.h>
 
 #include "map_parser.hpp"
 #include "utils.hpp"
@@ -80,3 +82,48 @@ int Utils::forkAndInvoke(const std::function<int()> &lambda)
     waitpid(pid, &status, 0);
     return status;
 }
+
+constexpr off_t EXT_SUPERBLOCK_OFFSET = 0x400;
+constexpr off_t EXT_MAGIC_OFFSET = 0x38;
+constexpr off_t EXT_ERRORS_OFFSET = 0x3C;
+constexpr uint16_t EXT_MAGIC = 0xEF53;
+
+const char *Utils::getExtErrorsBehavior(const Parsers::mountinfo_entry &entry)
+{
+    auto fs_type = entry.getFilesystemType();
+    if (fs_type != "ext2" && fs_type != "ext3" && fs_type != "ext4")
+        return nullptr;
+
+    std::ifstream file(entry.getMountSource(), std::ios::binary);
+    if (!file)
+        return nullptr;
+
+    uint16_t magic;
+    file.seekg(EXT_SUPERBLOCK_OFFSET + EXT_MAGIC_OFFSET, std::ios::beg);
+    file.read(reinterpret_cast<char *>(&magic), sizeof(magic));
+    if (!file || file.gcount() != sizeof(magic))
+        return nullptr;
+    magic = le16toh(magic);
+
+    if (magic != EXT_MAGIC)
+        return nullptr;
+
+    uint16_t errors;
+    file.seekg(EXT_SUPERBLOCK_OFFSET + EXT_ERRORS_OFFSET, std::ios::beg);
+    file.read(reinterpret_cast<char *>(&errors), sizeof(errors));
+    if (!file || file.gcount() != sizeof(errors))
+        return nullptr;
+    errors = le16toh(errors);
+
+    switch (errors)
+    {
+    case 1:
+        return "continue";
+    case 2:
+        return "remount-ro";
+    case 3:
+        return "panic";
+    default:
+        return nullptr;
+    }
+}