commit f442848000f08e7adf108b6c11bff1dfd744d456
author Bowgo Tsai <bowgotsai@google.com> Mon Jan 20 18:03:58 2020 +0800
committer Bowgo Tsai <bowgotsai@google.com> Thu Feb 13 15:15:20 2020 +0800
tree e6d9dc0ecb8de42b5dda03d09d1c2e21f52f9862
parent fdafa785d2ad1f4a8f28ffb1e918d8d6bf35d48d

Preserving /avb/* keys to /metadata

Those keys will be used for key revocation check by DSU installation
service. Note that failing to copy those keys to /metadata is NOT fatal,
because it is auxiliary to perform public key matching prior to booting
into DSU images on next boot. The actual key matching will still be done
on next DSU boot.

Bug: 146910547
Test: boot device, checks the avb keys are copied to /metadata/gsi/dsu/avb/.
Change-Id: I25a4eba82e84288bac7a859205c920628a063651

init/first_stage_mount.cpp

diff --git a/init/first_stage_mount.cpp b/init/first_stage_mount.cpp
index 21663e6..622e457 100644
--- a/init/first_stage_mount.cpp
+++ b/init/first_stage_mount.cpp
@@ -21,6 +21,7 @@
 #include <unistd.h>
 
 #include <chrono>
+#include <filesystem>
 #include <map>
 #include <memory>
 #include <set>
@@ -99,7 +100,11 @@
     void GetDmLinearMetadataDevice(std::set<std::string>* devices);
     bool InitDmLinearBackingDevices(const android::fs_mgr::LpMetadata& metadata);
     void UseDsuIfPresent();
+    // Reads all fstab.avb_keys from the ramdisk for first-stage mount.
     void PreloadAvbKeys();
+    // Copies /avb/*.avbpubkey used for DSU from the ramdisk to /metadata for key
+    // revocation check by DSU installation service.
+    void CopyDsuAvbKeys();
 
     ListenerAction UeventCallback(const Uevent& uevent, std::set<std::string>* required_devices);
 
@@ -595,7 +600,12 @@
         return entry.mount_point == "/metadata";
     });
     if (metadata_partition != fstab_.end()) {
-        MountPartition(metadata_partition, true /* erase_same_mounts */);
+        if (MountPartition(metadata_partition, true /* erase_same_mounts */)) {
+            // Copies DSU AVB keys from the ramdisk to /metadata.
+            // Must be done before the following TrySwitchSystemAsRoot().
+            // Otherwise, ramdisk will be inaccessible after switching root.
+            CopyDsuAvbKeys();
+        }
     }
 
     if (!CreateLogicalPartitions()) return false;
@@ -663,6 +673,27 @@
     return true;
 }
 
+// Preserves /avb/*.avbpubkey to /metadata/gsi/dsu/avb/, so they can be used for
+// key revocation check by DSU installation service.  Note that failing to
+// copy files to /metadata is NOT fatal, because it is auxiliary to perform
+// public key matching before booting into DSU images on next boot. The actual
+// public key matching will still be done on next boot to DSU.
+void FirstStageMount::CopyDsuAvbKeys() {
+    std::error_code ec;
+    // Removing existing keys in gsi::kDsuAvbKeyDir as they might be stale.
+    std::filesystem::remove_all(gsi::kDsuAvbKeyDir, ec);
+    if (ec) {
+        LOG(ERROR) << "Failed to remove directory " << gsi::kDsuAvbKeyDir << ": " << ec.message();
+    }
+    // Copy keys from the ramdisk /avb/* to gsi::kDsuAvbKeyDir.
+    static constexpr char kRamdiskAvbKeyDir[] = "/avb";
+    std::filesystem::copy(kRamdiskAvbKeyDir, gsi::kDsuAvbKeyDir, ec);
+    if (ec) {
+        LOG(ERROR) << "Failed to copy " << kRamdiskAvbKeyDir << " into " << gsi::kDsuAvbKeyDir
+                   << ": " << ec.message();
+    }
+}
+
 void FirstStageMount::UseDsuIfPresent() {
     std::string error;
 

init/selinux.cpp

diff --git a/init/selinux.cpp b/init/selinux.cpp
index 41007c1..c5b7576 100644
--- a/init/selinux.cpp
+++ b/init/selinux.cpp
@@ -65,6 +65,7 @@
 #include <android-base/parseint.h>
 #include <android-base/unique_fd.h>
 #include <fs_avb/fs_avb.h>
+#include <libgsi/libgsi.h>
 #include <selinux/android.h>
 
 #include "debug_ramdisk.h"
@@ -533,6 +534,8 @@
     selinux_android_restorecon("/apex", 0);
 
     selinux_android_restorecon("/linkerconfig", 0);
+
+    selinux_android_restorecon(gsi::kDsuAvbKeyDir, SELINUX_ANDROID_RESTORECON_RECURSE);
 }
 
 int SelinuxKlogCallback(int type, const char* fmt, ...) {