From f2cb3c38fea6b66bbe6d836a44b290f38ddfc573 Mon Sep 17 00:00:00 2001
From: topjohnwu <topjohnwu@gmail.com>
Date: Tue, 12 Jan 2021 22:50:55 -0800
Subject: [PATCH] Update mmap implementation

Always map memory as writable, but private when read-only
---
 native/jni/init/getinfo.cpp  |  2 +-
 native/jni/init/init.hpp     |  4 ++--
 native/jni/init/mount.cpp    | 10 +++++-----
 native/jni/init/raw_data.cpp | 30 +++++++++---------------------
 native/jni/init/raw_data.hpp | 34 +++++++++++++---------------------
 native/jni/init/rootdir.cpp  | 10 +++++-----
 native/jni/init/twostage.cpp |  4 ++--
 native/jni/utils/files.cpp   | 18 ++++++++++++++++--
 native/jni/utils/files.hpp   | 19 +++++--------------
 9 files changed, 58 insertions(+), 73 deletions(-)

diff --git a/native/jni/init/getinfo.cpp b/native/jni/init/getinfo.cpp
index 58524e82a..52d492736 100644
--- a/native/jni/init/getinfo.cpp
+++ b/native/jni/init/getinfo.cpp
@@ -213,6 +213,6 @@ bool check_two_stage() {
     if (access("/system/bin/init", F_OK) == 0)
         return true;
     // If we still have no indication, parse the original init and see what's up
-    auto init = raw_data::mmap_ro("/.backup/init");
+    auto init = mmap_data::ro("/.backup/init");
     return init.contains("selinux_setup");
 }
diff --git a/native/jni/init/init.hpp b/native/jni/init/init.hpp
index 0642a5fd5..b1cbcb722 100644
--- a/native/jni/init/init.hpp
+++ b/native/jni/init/init.hpp
@@ -54,8 +54,8 @@ public:
 
 class MagiskInit : public BaseInit {
 protected:
-    auto_data<HEAP> self;
-    auto_data<HEAP> config;
+    mmap_data self;
+    mmap_data config;
     std::string custom_rules_dir;
 
     void mount_with_dt();
diff --git a/native/jni/init/mount.cpp b/native/jni/init/mount.cpp
index a32da3754..e9f33c079 100644
--- a/native/jni/init/mount.cpp
+++ b/native/jni/init/mount.cpp
@@ -289,7 +289,7 @@ success:
 }
 
 void RootFSInit::early_mount() {
-    self = raw_data::read("/init");
+    self = mmap_data::ro("/init");
 
     LOGD("Restoring /init\n");
     rename("/.backup/init", "/init");
@@ -301,9 +301,9 @@ void SARBase::backup_files() {
     if (access("/overlay.d", F_OK) == 0)
         backup_folder("/overlay.d", overlays);
 
-    self = raw_data::read("/proc/self/exe");
+    self = mmap_data::ro("/proc/self/exe");
     if (access("/.backup/.magisk", R_OK) == 0)
-        config = raw_data::read("/.backup/.magisk");
+        config = mmap_data::ro("/.backup/.magisk");
 }
 
 void SARBase::mount_system_root() {
@@ -346,7 +346,7 @@ void SARInit::early_mount() {
     switch_root("/system_root");
 
     {
-        auto init = raw_data::mmap_ro("/init");
+        auto init = mmap_data::ro("/init");
         is_two_stage = init.contains("selinux_setup");
     }
     LOGD("is_two_stage: [%d]\n", is_two_stage);
@@ -383,7 +383,7 @@ void BaseInit::exec_init() {
 static void patch_socket_name(const char *path) {
     char rstr[16];
     gen_rand_str(rstr, sizeof(rstr));
-    auto bin = raw_data::mmap_rw(path);
+    auto bin = mmap_data::rw(path);
     bin.patch({ make_pair(MAIN_SOCKET, rstr) });
 }
 
diff --git a/native/jni/init/raw_data.cpp b/native/jni/init/raw_data.cpp
index 1164e1e18..3fa1027ee 100644
--- a/native/jni/init/raw_data.cpp
+++ b/native/jni/init/raw_data.cpp
@@ -2,7 +2,7 @@
 
 using namespace std;
 
-int data_holder::patch(str_pairs list) {
+int mmap_data::patch(str_pairs list) {
     if (buf == nullptr)
         return 0;
     int count = 0;
@@ -20,7 +20,7 @@ int data_holder::patch(str_pairs list) {
     return count;
 }
 
-bool data_holder::contains(string_view pattern) {
+bool mmap_data::contains(string_view pattern) {
     if (buf == nullptr)
         return false;
     for (uint8_t *p = buf, *eof = buf + sz; p < eof; ++p) {
@@ -32,33 +32,21 @@ bool data_holder::contains(string_view pattern) {
     return false;
 }
 
-void data_holder::consume(data_holder &other) {
+void mmap_data::consume(mmap_data &other) {
     buf = other.buf;
     sz = other.sz;
     other.buf = nullptr;
     other.sz = 0;
 }
 
-auto_data<HEAP> raw_data::read(int fd) {
-    auto_data<HEAP> data;
-    fd_full_read(fd, data.buf, data.sz);
+mmap_data mmap_data::rw(const char *name) {
+    mmap_data data;
+    mmap_rw(name, data.buf, data.sz);
     return data;
 }
 
-auto_data<HEAP> raw_data::read(const char *name) {
-    auto_data<HEAP> data;
-    full_read(name, data.buf, data.sz);
-    return data;
-}
-
-auto_data<MMAP> raw_data::mmap_rw(const char *name) {
-    auto_data<MMAP> data;
-    ::mmap_rw(name, data.buf, data.sz);
-    return data;
-}
-
-auto_data<MMAP> raw_data::mmap_ro(const char *name) {
-    auto_data<MMAP> data;
-    ::mmap_ro(name, data.buf, data.sz);
+mmap_data mmap_data::ro(const char *name) {
+    mmap_data data;
+    mmap_ro(name, data.buf, data.sz);
     return data;
 }
diff --git a/native/jni/init/raw_data.hpp b/native/jni/init/raw_data.hpp
index 049e05094..6732ea826 100644
--- a/native/jni/init/raw_data.hpp
+++ b/native/jni/init/raw_data.hpp
@@ -2,31 +2,23 @@
 
 #include <utils.hpp>
 
-struct data_holder {
+struct mmap_data {
     uint8_t *buf = nullptr;
     size_t sz = 0;
+
+    mmap_data() = default;
+    mmap_data(const mmap_data&) = delete;
+    mmap_data(mmap_data &&other) { consume(other); }
+    ~mmap_data() { if (buf) munmap(buf, sz); }
+    mmap_data& operator=(mmap_data &&other) { consume(other); return *this; }
+
     using str_pairs = std::initializer_list<std::pair<std::string_view, std::string_view>>;
     int patch(str_pairs list);
     bool contains(std::string_view pattern);
-protected:
-    void consume(data_holder &other);
-};
 
-enum data_type { HEAP, MMAP };
-template <data_type T>
-struct auto_data : public data_holder {
-    auto_data<T>() = default;
-    auto_data<T>(const auto_data&) = delete;
-    auto_data<T>(auto_data<T> &&other) { consume(other); }
-    ~auto_data<T>() {}
-    auto_data<T>& operator=(auto_data<T> &&other) { consume(other); return *this; }
-};
-template <> inline auto_data<MMAP>::~auto_data<MMAP>() { if (buf) munmap(buf, sz); }
-template <> inline auto_data<HEAP>::~auto_data<HEAP>() { free(buf); }
+    static mmap_data rw(const char *name);
+    static mmap_data ro(const char *name);
 
-namespace raw_data {
-    auto_data<HEAP> read(const char *name);
-    auto_data<HEAP> read(int fd);
-    auto_data<MMAP> mmap_rw(const char *name);
-    auto_data<MMAP> mmap_ro(const char *name);
-}
+private:
+    void consume(mmap_data &other);
+};
diff --git a/native/jni/init/rootdir.cpp b/native/jni/init/rootdir.cpp
index 807babb8c..a65771a6d 100644
--- a/native/jni/init/rootdir.cpp
+++ b/native/jni/init/rootdir.cpp
@@ -218,7 +218,7 @@ void SARBase::patch_rootdir() {
     int patch_count;
     {
         int src = xopen("/init", O_RDONLY | O_CLOEXEC);
-        auto init = raw_data::read(src);
+        auto init = mmap_data::ro("/init");
         patch_count = init.patch({
             make_pair(SPLIT_PLAT_CIL, "xxx"), /* Force loading monolithic sepolicy */
             make_pair(MONOPOLICY, sepol)      /* Redirect /sepolicy to custom path */
@@ -233,7 +233,7 @@ void SARBase::patch_rootdir() {
 
     if (patch_count != 2 && access(LIBSELINUX, F_OK) == 0) {
         // init is dynamically linked, need to patch libselinux
-        auto lib = raw_data::read(LIBSELINUX);
+        auto lib = mmap_data::ro(LIBSELINUX);
         lib.patch({make_pair(MONOPOLICY, sepol)});
         xmkdirs(dirname(ROOTOVL LIBSELINUX), 0755);
         int dest = xopen(ROOTOVL LIBSELINUX, O_CREAT | O_WRONLY | O_CLOEXEC, 0);
@@ -301,7 +301,7 @@ void RootFSInit::patch_rootfs() {
     }
 
     if (patch_sepolicy("/sepolicy")) {
-        auto init = raw_data::mmap_rw("/init");
+        auto init = mmap_data::rw("/init");
         init.patch({ make_pair(SPLIT_PLAT_CIL, "xxx") });
     }
 
@@ -331,8 +331,8 @@ void MagiskProxy::start() {
     xmount(nullptr, "/", nullptr, MS_REMOUNT, nullptr);
 
     // Backup stuffs before removing them
-    self = raw_data::read("/sbin/magisk");
-    config = raw_data::read("/.backup/.magisk");
+    self = mmap_data::ro("/sbin/magisk");
+    config = mmap_data::ro("/.backup/.magisk");
     char custom_rules_dir[64];
     custom_rules_dir[0] = '\0';
     xreadlink(TMP_RULESDIR, custom_rules_dir, sizeof(custom_rules_dir));
diff --git a/native/jni/init/twostage.cpp b/native/jni/init/twostage.cpp
index 2d6f505c0..25265c0ca 100644
--- a/native/jni/init/twostage.cpp
+++ b/native/jni/init/twostage.cpp
@@ -114,7 +114,7 @@ void FirstStageInit::prepare() {
         }
 
         // Patch init to force IsDtFstabCompatible() return false
-        auto init = raw_data::mmap_rw("/init");
+        auto init = mmap_data::rw("/init");
         init.patch({ make_pair("android,fstab", "xxx") });
     }
 
@@ -150,7 +150,7 @@ void SARInit::first_stage_prep() {
     int src = xopen("/init", O_RDONLY);
     int dest = xopen("/dev/init", O_CREAT | O_WRONLY, 0);
     {
-        auto init = raw_data::read(src);
+        auto init = mmap_data::ro("/init");
         init.patch({ make_pair(INIT_PATH, REDIR_PATH) });
         write(dest, init.buf, init.sz);
         fclone_attr(src, dest);
diff --git a/native/jni/utils/files.cpp b/native/jni/utils/files.cpp
index ff98df7fa..f4657c876 100644
--- a/native/jni/utils/files.cpp
+++ b/native/jni/utils/files.cpp
@@ -279,7 +279,6 @@ void *__mmap(const char *filename, size_t *size, bool rw) {
         return nullptr;
     }
     struct stat st;
-    void *buf;
     if (fstat(fd, &st)) {
         *size = 0;
         return nullptr;
@@ -288,7 +287,9 @@ void *__mmap(const char *filename, size_t *size, bool rw) {
         ioctl(fd, BLKGETSIZE64, size);
     else
         *size = st.st_size;
-    buf = *size > 0 ? xmmap(nullptr, *size, PROT_READ | (rw ? PROT_WRITE : 0), MAP_SHARED, fd, 0) : nullptr;
+    void *buf = *size > 0 ?
+            xmmap(nullptr, *size, PROT_READ | PROT_WRITE, rw ? MAP_SHARED : MAP_PRIVATE, fd, 0) :
+            nullptr;
     close(fd);
     return buf;
 }
@@ -437,3 +438,16 @@ sDIR make_dir(DIR *dp) {
 sFILE make_file(FILE *fp) {
     return sFILE(fp, [](FILE *fp){ return fp ? fclose(fp) : 1; });
 }
+
+raw_file::raw_file(raw_file &&o) {
+    path.swap(o.path);
+    attr = o.attr;
+    buf = o.buf;
+    sz = o.sz;
+    o.buf = nullptr;
+    o.sz = 0;
+}
+
+raw_file::~raw_file() {
+    free(buf);
+}
diff --git a/native/jni/utils/files.hpp b/native/jni/utils/files.hpp
index 465f176b4..e5e38f898 100644
--- a/native/jni/utils/files.hpp
+++ b/native/jni/utils/files.hpp
@@ -21,22 +21,13 @@ struct file_attr {
 struct raw_file {
     std::string path;
     file_attr attr;
-    uint8_t *buf = nullptr;
-    size_t sz = 0;
+    uint8_t *buf;
+    size_t sz;
 
-    raw_file() = default;
+    raw_file() : attr({}), buf(nullptr), sz(0) {}
     raw_file(const raw_file&) = delete;
-    raw_file(raw_file &&d) {
-        path = std::move(d.path);
-        attr = d.attr;
-        buf = d.buf;
-        sz = d.sz;
-        d.buf = nullptr;
-        d.sz = 0;
-    }
-    ~raw_file() {
-        free(buf);
-    }
+    raw_file(raw_file &&o);
+    ~raw_file();
 };
 
 ssize_t fd_path(int fd, char *path, size_t size);