init: chroot from recovery to /first_stage_ramdisk

When using the recovery image as a trampoline to boot the system,
first chroot from the recovery image to /first_stage_ramdisk, to
minimize differences between these two boot paths.

Primary motivation is due to the fact that the basename of each mount
point is used by device-manager to name its nodes, and the previous
code that created used /system_recovery_mount as the mount point for
system.img broke AVB.  Instead of hacking around that issue, this
change unified mounting for the recovery trampoline and true first
stage ramdisk paths.

Bug: 114062208
Test: AVB works with blueline_mainline
Change-Id: Iffb154962b6e160150917e068f1e7d0bf7cb84e7

init/first_stage_mount.cpp

@@ -17,6 +17,7 @@
 #include "first_stage_mount.h"
 
 #include <stdlib.h>
+#include <sys/mount.h>
 #include <unistd.h>
 
 #include <chrono>
@@ -122,18 +123,8 @@ static inline bool IsDtVbmetaCompatible() {
     return is_android_dt_value_expected("vbmeta/compatible", "android,vbmeta");
 }
 
-static bool ForceNormalBoot() {
-    static bool force_normal_boot = []() {
-        std::string cmdline;
-        android::base::ReadFileToString("/proc/cmdline", &cmdline);
-        return cmdline.find("androidboot.force_normal_boot=1") != std::string::npos;
-    }();
-
-    return force_normal_boot;
-}
-
 static bool IsRecoveryMode() {
-    return !ForceNormalBoot() && access("/system/bin/recovery", F_OK) == 0;
+    return access("/system/bin/recovery", F_OK) == 0;
 }
 
 // Class Definitions
@@ -371,16 +362,11 @@ bool FirstStageMount::MountPartitions() {
                          [](const auto& rec) { return rec->mount_point == "/system"s; });
 
     if (system_partition != mount_fstab_recs_.end()) {
-        if (ForceNormalBoot()) {
-            free((*system_partition)->mount_point);
-            (*system_partition)->mount_point = strdup("/system_recovery_mount");
-        }
-
         if (!MountPartition(*system_partition)) {
             return false;
         }
 
-        SwitchRoot((*system_partition)->mount_point);
+        SwitchRoot((*system_partition)->mount_point, true);
 
         mount_fstab_recs_.erase(system_partition);
     }

init/init_first_stage.cpp

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include <dirent.h>
+#include <fcntl.h>
 #include <paths.h>
 #include <stdlib.h>
 #include <sys/mount.h>
@@ -26,19 +28,72 @@
 #include <vector>
 
 #include <android-base/chrono_utils.h>
+#include <android-base/file.h>
 #include <android-base/logging.h>
 #include <cutils/android_reboot.h>
 #include <private/android_filesystem_config.h>
 
 #include "first_stage_mount.h"
 #include "reboot_utils.h"
+#include "switch_root.h"
 #include "util.h"
 
 using android::base::boot_clock;
 
+using namespace std::literals;
+
 namespace android {
 namespace init {
 
+namespace {
+
+void FreeRamdisk(DIR* dir, dev_t dev) {
+    int dfd = dirfd(dir);
+
+    dirent* de;
+    while ((de = readdir(dir)) != nullptr) {
+        if (de->d_name == "."s || de->d_name == ".."s) {
+            continue;
+        }
+
+        bool is_dir = false;
+
+        if (de->d_type == DT_DIR || de->d_type == DT_UNKNOWN) {
+            struct stat info;
+            if (fstatat(dfd, de->d_name, &info, AT_SYMLINK_NOFOLLOW) != 0) {
+                continue;
+            }
+
+            if (info.st_dev != dev) {
+                continue;
+            }
+
+            if (S_ISDIR(info.st_mode)) {
+                is_dir = true;
+                auto fd = openat(dfd, de->d_name, O_RDONLY | O_DIRECTORY);
+                if (fd >= 0) {
+                    auto subdir =
+                            std::unique_ptr<DIR, decltype(&closedir)>{fdopendir(fd), closedir};
+                    if (subdir) {
+                        FreeRamdisk(subdir.get(), dev);
+                    } else {
+                        close(fd);
+                    }
+                }
+            }
+        }
+        unlinkat(dfd, de->d_name, is_dir ? AT_REMOVEDIR : 0);
+    }
+}
+
+bool ForceNormalBoot() {
+    std::string cmdline;
+    android::base::ReadFileToString("/proc/cmdline", &cmdline);
+    return cmdline.find("androidboot.force_normal_boot=1") != std::string::npos;
+}
+
+}  // namespace
+
 int main(int argc, char** argv) {
     if (REBOOT_BOOTLOADER_ON_PANIC) {
         InstallRebootSignalHandlers();
@@ -117,10 +172,36 @@ int main(int argc, char** argv) {
 
     LOG(INFO) << "init first stage started!";
 
+    auto old_root_dir = std::unique_ptr<DIR, decltype(&closedir)>{opendir("/"), closedir};
+    if (!old_root_dir) {
+        PLOG(ERROR) << "Could not opendir(\"/\"), not freeing ramdisk";
+    }
+
+    struct stat old_root_info;
+    if (stat("/", &old_root_info) != 0) {
+        PLOG(ERROR) << "Could not stat(\"/\"), not freeing ramdisk";
+        old_root_dir.reset();
+    }
+
+    if (ForceNormalBoot()) {
+        mkdir("/first_stage_ramdisk", 0755);
+        SwitchRoot("/first_stage_ramdisk", false);
+    }
+
     if (!DoFirstStageMount()) {
         LOG(FATAL) << "Failed to mount required partitions early ...";
     }
 
+    struct stat new_root_info;
+    if (stat("/", &new_root_info) != 0) {
+        PLOG(ERROR) << "Could not stat(\"/\"), not freeing ramdisk";
+        old_root_dir.reset();
+    }
+
+    if (old_root_dir && old_root_info.st_dev != new_root_info.st_dev) {
+        FreeRamdisk(old_root_dir.get(), old_root_info.st_dev);
+    }
+
     SetInitAvbVersionInRecovery();
 
     static constexpr uint32_t kNanosecondsPerMillisecond = 1e6;

init/switch_root.cpp

@@ -16,7 +16,6 @@
 
 #include "switch_root.h"
 
-#include <dirent.h>
 #include <fcntl.h>
 #include <mntent.h>
 #include <sys/mount.h>
@@ -35,45 +34,6 @@ namespace init {
 
 namespace {
 
-void FreeRamdisk(DIR* dir, dev_t dev) {
-    int dfd = dirfd(dir);
-
-    dirent* de;
-    while ((de = readdir(dir)) != nullptr) {
-        if (de->d_name == "."s || de->d_name == ".."s) {
-            continue;
-        }
-
-        bool is_dir = false;
-
-        if (de->d_type == DT_DIR || de->d_type == DT_UNKNOWN) {
-            struct stat info;
-            if (fstatat(dfd, de->d_name, &info, AT_SYMLINK_NOFOLLOW) != 0) {
-                continue;
-            }
-
-            if (info.st_dev != dev) {
-                continue;
-            }
-
-            if (S_ISDIR(info.st_mode)) {
-                is_dir = true;
-                auto fd = openat(dfd, de->d_name, O_RDONLY | O_DIRECTORY);
-                if (fd >= 0) {
-                    auto subdir =
-                            std::unique_ptr<DIR, decltype(&closedir)>{fdopendir(fd), closedir};
-                    if (subdir) {
-                        FreeRamdisk(subdir.get(), dev);
-                    } else {
-                        close(fd);
-                    }
-                }
-            }
-        }
-        unlinkat(dfd, de->d_name, is_dir ? AT_REMOVEDIR : 0);
-    }
-}
-
 std::vector<std::string> GetMounts(const std::string& new_root) {
     auto fp = std::unique_ptr<std::FILE, decltype(&endmntent)>{setmntent("/proc/mounts", "re"),
                                                                endmntent};
@@ -109,42 +69,32 @@ std::vector<std::string> GetMounts(const std::string& new_root) {
 
 }  // namespace
 
-void SwitchRoot(const std::string& new_root) {
+void SwitchRoot(const std::string& new_root, bool move_root_mount) {
     auto mounts = GetMounts(new_root);
 
+    LOG(INFO) << "Switching root to '" << new_root << "'";
+
     for (const auto& mount_path : mounts) {
         auto new_mount_path = new_root + mount_path;
+        mkdir(new_mount_path.c_str(), 0755);
         if (mount(mount_path.c_str(), new_mount_path.c_str(), nullptr, MS_MOVE, nullptr) != 0) {
             PLOG(FATAL) << "Unable to move mount at '" << mount_path << "'";
         }
     }
 
-    auto old_root_dir = std::unique_ptr<DIR, decltype(&closedir)>{opendir("/"), closedir};
-    if (!old_root_dir) {
-        PLOG(ERROR) << "Could not opendir(\"/\"), not freeing ramdisk";
-    }
-
-    struct stat old_root_info;
-    if (stat("/", &old_root_info) != 0) {
-        PLOG(ERROR) << "Could not stat(\"/\"), not freeing ramdisk";
-        old_root_dir.reset();
-    }
-
     if (chdir(new_root.c_str()) != 0) {
         PLOG(FATAL) << "Could not chdir to new_root, '" << new_root << "'";
     }
 
-    if (mount(new_root.c_str(), "/", nullptr, MS_MOVE, nullptr) != 0) {
-        PLOG(FATAL) << "Unable to move root mount to new_root, '" << new_root << "'";
+    if (move_root_mount) {
+        if (mount(new_root.c_str(), "/", nullptr, MS_MOVE, nullptr) != 0) {
+            PLOG(FATAL) << "Unable to move root mount to new_root, '" << new_root << "'";
+        }
     }
 
     if (chroot(".") != 0) {
         PLOG(FATAL) << "Unable to chroot to new root";
     }
-
-    if (old_root_dir) {
-        FreeRamdisk(old_root_dir.get(), old_root_info.st_dev);
-    }
 }
 
 }  // namespace init

init/switch_root.h

@@ -21,7 +21,7 @@
 namespace android {
 namespace init {
 
-void SwitchRoot(const std::string& new_root);
+void SwitchRoot(const std::string& new_root, bool move_root_mount);
 
 }  // namespace init
 }  // namespace android