adb: add overlayfs handling for readonly system filesystems

adb verity-on setup overlayfs directories, do not skip if verity
feature not configured for device.

adb verity-off teardown overlayfs directories, do not skip if verity
feature not configured for device.

adb remount setup overlayfs directories and mount if possible, and
do so without a reboot if possible.

Test: compile
Bug: 109821005
Bug: 110985612
Change-Id: I28c4c23fea44b886c5523f0286a523f0b0485df0
diff --git a/adb/daemon/remount_service.cpp b/adb/daemon/remount_service.cpp
index 0e79d82..f7017dd 100644
--- a/adb/daemon/remount_service.cpp
+++ b/adb/daemon/remount_service.cpp
@@ -30,6 +30,7 @@
 #include <sys/vfs.h>
 #include <unistd.h>
 
+#include <memory>
 #include <set>
 #include <string>
 #include <vector>
@@ -38,28 +39,30 @@
 #include <bootloader_message/bootloader_message.h>
 #include <cutils/android_reboot.h>
 #include <ext4_utils/ext4_utils.h>
+#include <fs_mgr.h>
+#include <fs_mgr_overlayfs.h>
 
 #include "adb.h"
 #include "adb_io.h"
 #include "adb_unique_fd.h"
 #include "adb_utils.h"
-#include "fs_mgr.h"
 #include "set_verity_enable_state_service.h"
 
-// Returns the device used to mount a directory in /proc/mounts.
+// Returns the last device used to mount a directory in /proc/mounts.
+// This will find overlayfs entry where upperdir=lowerdir, to make sure
+// remount is associated with the correct directory.
 static std::string find_proc_mount(const char* dir) {
     std::unique_ptr<FILE, int(*)(FILE*)> fp(setmntent("/proc/mounts", "r"), endmntent);
-    if (!fp) {
-        return "";
-    }
+    std::string mnt_fsname;
+    if (!fp) return mnt_fsname;
 
     mntent* e;
     while ((e = getmntent(fp.get())) != nullptr) {
         if (strcmp(dir, e->mnt_dir) == 0) {
-            return e->mnt_fsname;
+            mnt_fsname = e->mnt_fsname;
         }
     }
-    return "";
+    return mnt_fsname;
 }
 
 // Returns the device used to mount a directory in the fstab.
@@ -81,6 +84,7 @@
 }
 
 bool make_block_device_writable(const std::string& dev) {
+    if ((dev == "overlay") || (dev == "overlayfs")) return true;
     int fd = unix_open(dev.c_str(), O_RDONLY | O_CLOEXEC);
     if (fd == -1) {
         return false;
@@ -234,6 +238,14 @@
         partitions.push_back("/system");
     }
 
+    bool verity_enabled = (system_verified || vendor_verified);
+
+    // If we can use overlayfs, lets get it in place first
+    // before we struggle with determining deduplication operations.
+    if (!verity_enabled && fs_mgr_overlayfs_setup() && fs_mgr_overlayfs_mount_all()) {
+        WriteFdExactly(fd.get(), "overlayfs mounted\n");
+    }
+
     // Find partitions that are deduplicated, and can be un-deduplicated.
     std::set<std::string> dedup;
     for (const auto& partition : partitions) {
@@ -246,8 +258,6 @@
         }
     }
 
-    bool verity_enabled = (system_verified || vendor_verified);
-
     // Reboot now if the user requested it (and an operation needs a reboot).
     if (user_requested_reboot) {
         if (!dedup.empty() || verity_enabled) {
diff --git a/adb/daemon/set_verity_enable_state_service.cpp b/adb/daemon/set_verity_enable_state_service.cpp
index 2b6ec21..3676de5 100644
--- a/adb/daemon/set_verity_enable_state_service.cpp
+++ b/adb/daemon/set_verity_enable_state_service.cpp
@@ -19,6 +19,7 @@
 #include "set_verity_enable_state_service.h"
 #include "sysdeps.h"
 
+#include <errno.h>
 #include <fcntl.h>
 #include <inttypes.h>
 #include <libavb_user/libavb_user.h>
@@ -28,12 +29,14 @@
 
 #include <android-base/properties.h>
 #include <android-base/stringprintf.h>
+#include <fs_mgr.h>
+#include <fs_mgr_overlayfs.h>
+#include <fstab/fstab.h>
 #include <log/log_properties.h>
 
 #include "adb.h"
 #include "adb_io.h"
 #include "adb_unique_fd.h"
-#include "fs_mgr.h"
 #include "remount_service.h"
 
 #include "fec/io.h"
@@ -46,6 +49,10 @@
 static const bool kAllowDisableVerity = false;
 #endif
 
+void suggest_run_adb_root(int fd) {
+    if (getuid() != 0) WriteFdExactly(fd, "Maybe run adb root?\n");
+}
+
 /* Turn verity on/off */
 static bool set_verity_enabled_state(int fd, const char* block_device, const char* mount_point,
                                      bool enable) {
@@ -59,7 +66,7 @@
 
     if (!fh) {
         WriteFdFmt(fd, "Could not open block device %s (%s).\n", block_device, strerror(errno));
-        WriteFdFmt(fd, "Maybe run adb root?\n");
+        suggest_run_adb_root(fd);
         return false;
     }
 
@@ -87,6 +94,17 @@
         return false;
     }
 
+    auto change = false;
+    errno = 0;
+    if (enable ? fs_mgr_overlayfs_teardown(mount_point, &change)
+               : fs_mgr_overlayfs_setup(nullptr, mount_point, &change)) {
+        if (change) {
+            WriteFdFmt(fd, "%s overlayfs for %s\n", enable ? "disabling" : "using", mount_point);
+        }
+    } else if (errno) {
+        WriteFdFmt(fd, "Overlayfs %s for %s failed with error %s\n", enable ? "teardown" : "setup",
+                   mount_point, strerror(errno));
+    }
     WriteFdFmt(fd, "Verity %s on %s\n", enable ? "enabled" : "disabled", mount_point);
     return true;
 }
@@ -103,6 +121,22 @@
     return android::base::GetProperty("ro.boot.vbmeta.device_state", "") == "locked";
 }
 
+static bool overlayfs_setup(int fd, bool enable) {
+    auto change = false;
+    errno = 0;
+    if (enable ? fs_mgr_overlayfs_teardown(nullptr, &change)
+               : fs_mgr_overlayfs_setup(nullptr, nullptr, &change)) {
+        if (change) {
+            WriteFdFmt(fd, "%s overlayfs\n", enable ? "disabling" : "using");
+        }
+    } else if (errno) {
+        WriteFdFmt(fd, "Overlayfs %s failed with error %s\n", enable ? "teardown" : "setup",
+                   strerror(errno));
+        suggest_run_adb_root(fd);
+    }
+    return change;
+}
+
 /* Use AVB to turn verity on/off */
 static bool set_avb_verity_enabled_state(int fd, AvbOps* ops, bool enable_verity) {
     std::string ab_suffix = get_ab_suffix();
@@ -128,6 +162,7 @@
         return false;
     }
 
+    overlayfs_setup(fd, enable_verity);
     WriteFdFmt(fd, "Successfully %s verity\n", enable_verity ? "enabled" : "disabled");
     return true;
 }
@@ -150,6 +185,7 @@
         }
 
         if (!android::base::GetBoolProperty("ro.secure", false)) {
+            overlayfs_setup(fd, enable);
             WriteFdExactly(fd.get(), "verity not enabled - ENG build\n");
             return;
         }
@@ -177,13 +213,14 @@
         // Not using AVB - assume VB1.0.
 
         // read all fstab entries at once from all sources
-        fstab = fs_mgr_read_fstab_default();
+        if (!fstab) fstab = fs_mgr_read_fstab_default();
         if (!fstab) {
-            WriteFdExactly(fd.get(), "Failed to read fstab\nMaybe run adb root?\n");
+            WriteFdExactly(fd.get(), "Failed to read fstab\n");
+            suggest_run_adb_root(fd.get());
             return;
         }
 
-        // Loop through entries looking for ones that vold manages.
+        // Loop through entries looking for ones that verity manages.
         for (int i = 0; i < fstab->num_entries; i++) {
             if (fs_mgr_is_verified(&fstab->recs[i])) {
                 if (set_verity_enabled_state(fd.get(), fstab->recs[i].blk_device,
@@ -193,6 +230,7 @@
             }
         }
     }
+    if (!any_changed) any_changed = overlayfs_setup(fd, enable);
 
     if (any_changed) {
         WriteFdExactly(fd.get(), "Now reboot your device for settings to take effect\n");