fskeyring & userspace reboot: support CE keys

During userspace reboot /data might be unmounted & remounted, meaning
that CE keys stored in fs-level keyring will be lost. In order to be
able to restore them, when installing new key to fs-level keyring, it's
also added to session-level keyring with type "fscrypt-provisioning".

Then when init_user0 is called during userspace reboot, vold will try to
load CE keys from the session-level keyring back into fs-level keyring
for all the users that were unlocked before the reboot.

If for any user vold fails to install the key, init_user0 will fail and
fallback to hard reboot will be triggered.

Test: set a pin pattern
Test: adb shell setprop sys.init.userdata_remount.force_umount 1
Test: adb shell svc power reboot userspace
Test: atest CtsUserspaceRebootHostSideTestCases
Bug: 143970043
Change-Id: I37603dc136c7ededc7b0381e4d730cb0ffd912b4

FsCrypt.cpp

@@ -378,6 +378,17 @@ static bool load_all_de_keys() {
     return true;
 }
 
+// Attempt to reinstall CE keys for users that we think are unlocked.
+static bool try_reload_ce_keys() {
+    for (const auto& it : s_ce_policies) {
+        if (!android::vold::reloadKeyFromSessionKeyring(DATA_MNT_POINT, it.second)) {
+            LOG(ERROR) << "Failed to load CE key from session keyring for user " << it.first;
+            return false;
+        }
+    }
+    return true;
+}
+
 bool fscrypt_initialize_systemwide_keys() {
     LOG(INFO) << "fscrypt_initialize_systemwide_keys";
 
@@ -444,6 +455,13 @@ bool fscrypt_init_user0() {
         fscrypt_unlock_user_key(0, 0, "!", "!");
     }
 
+    // In some scenarios (e.g. userspace reboot) we might unmount userdata
+    // without doing a hard reboot. If CE keys were stored in fs keyring then
+    // they will be lost after unmount. Attempt to re-install them.
+    if (fscrypt_is_native() && android::vold::isFsKeyringSupported()) {
+        if (!try_reload_ce_keys()) return false;
+    }
+
     return true;
 }
 

KeyUtil.cpp

@@ -155,7 +155,7 @@ static bool fscryptKeyring(key_serial_t* device_keyring) {
     return true;
 }
 
-// Add an encryption key to the legacy global session keyring.
+// Add an encryption key of type "logon" to the global session keyring.
 static bool installKeyLegacy(const KeyBuffer& key, const std::string& raw_ref) {
     // Place fscrypt_key into automatically zeroing buffer.
     KeyBuffer fsKeyBuffer(sizeof(fscrypt_key));
@@ -178,6 +178,32 @@ static bool installKeyLegacy(const KeyBuffer& key, const std::string& raw_ref) {
     return true;
 }
 
+// Installs fscrypt-provisioning key into session level kernel keyring.
+// This allows for the given key to be installed back into filesystem keyring.
+// For more context see reloadKeyFromSessionKeyring.
+static bool installProvisioningKey(const KeyBuffer& key, const std::string& ref,
+                                   const fscrypt_key_specifier& key_spec) {
+    key_serial_t device_keyring;
+    if (!fscryptKeyring(&device_keyring)) return false;
+
+    // Place fscrypt_provisioning_key_payload into automatically zeroing buffer.
+    KeyBuffer buf(sizeof(fscrypt_provisioning_key_payload) + key.size(), 0);
+    fscrypt_provisioning_key_payload& provisioning_key =
+            *reinterpret_cast<fscrypt_provisioning_key_payload*>(buf.data());
+    memcpy(provisioning_key.raw, key.data(), key.size());
+    provisioning_key.type = key_spec.type;
+
+    key_serial_t key_id = add_key("fscrypt-provisioning", ref.c_str(), (void*)&provisioning_key,
+                                  buf.size(), device_keyring);
+    if (key_id == -1) {
+        PLOG(ERROR) << "Failed to insert fscrypt-provisioning key for " << ref
+                    << " into session keyring";
+        return false;
+    }
+    LOG(DEBUG) << "Added fscrypt-provisioning key for " << ref << " to session keyring";
+    return true;
+}
+
 // Build a struct fscrypt_key_specifier for use in the key management ioctls.
 static bool buildKeySpecifier(fscrypt_key_specifier* spec, const EncryptionPolicy& policy) {
     switch (policy.options.version) {
@@ -205,6 +231,34 @@ static bool buildKeySpecifier(fscrypt_key_specifier* spec, const EncryptionPolic
     }
 }
 
+// Installs key into keyring of a filesystem mounted on |mountpoint|.
+//
+// It's callers responsibility to fill key specifier, and either arg->raw or arg->key_id.
+//
+// In case arg->key_spec.type equals to FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER
+// arg->key_spec.u.identifier will be populated with raw key reference generated
+// by kernel.
+//
+// For documentation on difference between arg->raw and arg->key_id see
+// https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#fs-ioc-add-encryption-key
+static bool installFsKeyringKey(const std::string& mountpoint, const EncryptionOptions& options,
+                                fscrypt_add_key_arg* arg) {
+    if (options.use_hw_wrapped_key) arg->flags |= FSCRYPT_ADD_KEY_FLAG_WRAPPED;
+
+    android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
+    if (fd == -1) {
+        PLOG(ERROR) << "Failed to open " << mountpoint << " to install key";
+        return false;
+    }
+
+    if (ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, arg) != 0) {
+        PLOG(ERROR) << "Failed to install fscrypt key to " << mountpoint;
+        return false;
+    }
+
+    return true;
+}
+
 bool installKey(const std::string& mountpoint, const EncryptionOptions& options,
                 const KeyBuffer& key, EncryptionPolicy* policy) {
     policy->options = options;
@@ -240,33 +294,24 @@ bool installKey(const std::string& mountpoint, const EncryptionOptions& options,
             return false;
     }
 
-    if (options.use_hw_wrapped_key) arg->flags |= FSCRYPT_ADD_KEY_FLAG_WRAPPED;
-    // Provide the raw key.
     arg->raw_size = key.size();
     memcpy(arg->raw, key.data(), key.size());
 
-    android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
+    if (!installFsKeyringKey(mountpoint, options, arg)) return false;
-    if (fd == -1) {
-        PLOG(ERROR) << "Failed to open " << mountpoint << " to install key";
-        return false;
-    }
-
-    if (ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, arg) != 0) {
-        PLOG(ERROR) << "Failed to install fscrypt key to " << mountpoint;
-        return false;
-    }
 
     if (arg->key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
         // Retrieve the key identifier that the kernel computed.
         policy->key_raw_ref =
                 std::string((char*)arg->key_spec.u.identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
     }
-    LOG(DEBUG) << "Installed fscrypt key with ref " << keyrefstring(policy->key_raw_ref) << " to "
+    std::string ref = keyrefstring(policy->key_raw_ref);
-               << mountpoint;
+    LOG(DEBUG) << "Installed fscrypt key with ref " << ref << " to " << mountpoint;
+
+    if (!installProvisioningKey(key, ref, arg->key_spec)) return false;
     return true;
 }
 
-// Remove an encryption key from the legacy global session keyring.
+// Remove an encryption key of type "logon" from the global session keyring.
 static bool evictKeyLegacy(const std::string& raw_ref) {
     key_serial_t device_keyring;
     if (!fscryptKeyring(&device_keyring)) return false;
@@ -289,6 +334,26 @@ static bool evictKeyLegacy(const std::string& raw_ref) {
     return success;
 }
 
+static bool evictProvisioningKey(const std::string& ref) {
+    key_serial_t device_keyring;
+    if (!fscryptKeyring(&device_keyring)) {
+        return false;
+    }
+
+    auto key_serial = keyctl_search(device_keyring, "fscrypt-provisioning", ref.c_str(), 0);
+    if (key_serial == -1 && errno != ENOKEY) {
+        PLOG(ERROR) << "Error searching session keyring for fscrypt-provisioning key for " << ref;
+        return false;
+    }
+
+    if (key_serial != -1 && keyctl_unlink(key_serial, device_keyring) != 0) {
+        PLOG(ERROR) << "Failed to unlink fscrypt-provisioning key for " << ref
+                    << " from session keyring";
+        return false;
+    }
+    return true;
+}
+
 bool evictKey(const std::string& mountpoint, const EncryptionPolicy& policy) {
     if (policy.options.version == 1 && !isFsKeyringSupported()) {
         return evictKeyLegacy(policy.key_raw_ref);
@@ -322,6 +387,8 @@ bool evictKey(const std::string& mountpoint, const EncryptionPolicy& policy) {
         LOG(ERROR) << "Files still open after removing key with ref " << ref
                    << ".  These files were not locked!";
     }
+
+    if (!evictProvisioningKey(ref)) return false;
     return true;
 }
 
@@ -343,5 +410,31 @@ bool retrieveOrGenerateKey(const std::string& key_path, const std::string& tmp_p
     return true;
 }
 
+bool reloadKeyFromSessionKeyring(const std::string& mountpoint, const EncryptionPolicy& policy) {
+    key_serial_t device_keyring;
+    if (!fscryptKeyring(&device_keyring)) {
+        return false;
+    }
+
+    std::string ref = keyrefstring(policy.key_raw_ref);
+    auto key_serial = keyctl_search(device_keyring, "fscrypt-provisioning", ref.c_str(), 0);
+    if (key_serial == -1) {
+        PLOG(ERROR) << "Failed to find fscrypt-provisioning key for " << ref
+                    << " in session keyring";
+        return false;
+    }
+
+    LOG(DEBUG) << "Installing fscrypt-provisioning key for " << ref << " back into " << mountpoint
+               << " fs-keyring";
+
+    struct fscrypt_add_key_arg arg;
+    memset(&arg, 0, sizeof(arg));
+    if (!buildKeySpecifier(&arg.key_spec, policy)) return false;
+    arg.key_id = key_serial;
+    if (!installFsKeyringKey(mountpoint, policy.options, &arg)) return false;
+
+    return true;
+}
+
 }  // namespace vold
 }  // namespace android

KeyUtil.h

@@ -51,11 +51,16 @@ bool isFsKeyringSupported(void);
 // on the specified filesystem using the specified encryption policy version.
 //
 // For v1 policies, we use FS_IOC_ADD_ENCRYPTION_KEY if the kernel supports it.
-// Otherwise we add the key to the legacy global session keyring.
+// Otherwise we add the key to the global session keyring as a "logon" key.
 //
 // For v2 policies, we always use FS_IOC_ADD_ENCRYPTION_KEY; it's the only way
 // the kernel supports.
 //
+// If kernel supports FS_IOC_ADD_ENCRYPTION_KEY, also installs key of
+// fscrypt-provisioning type to the global session keyring. This makes it
+// possible to unmount and then remount mountpoint without losing the file-based
+// key.
+//
 // Returns %true on success, %false on failure.  On success also sets *policy
 // to the EncryptionPolicy used to refer to this key.
 bool installKey(const std::string& mountpoint, const EncryptionOptions& options,
@@ -63,16 +68,20 @@ bool installKey(const std::string& mountpoint, const EncryptionOptions& options,
 
 // Evict a file-based encryption key from the kernel.
 //
-// We use FS_IOC_REMOVE_ENCRYPTION_KEY if the kernel supports it.  Otherwise we
+// This undoes the effect of installKey().
-// remove the key from the legacy global session keyring.
 //
-// In the latter case, the caller is responsible for dropping caches.
+// If the kernel doesn't support the filesystem-level keyring, the caller is
+// responsible for dropping caches.
 bool evictKey(const std::string& mountpoint, const EncryptionPolicy& policy);
 
 bool retrieveOrGenerateKey(const std::string& key_path, const std::string& tmp_path,
                            const KeyAuthentication& key_authentication, const KeyGeneration& gen,
                            KeyBuffer* key, bool keepOld = true);
 
+// Re-installs a file-based encryption key of fscrypt-provisioning type from the
+// global session keyring back into fs keyring of the mountpoint.
+bool reloadKeyFromSessionKeyring(const std::string& mountpoint, const EncryptionPolicy& policy);
+
 }  // namespace vold
 }  // namespace android
 

fscrypt_uapi.h

@@ -9,11 +9,19 @@
 struct sys_fscrypt_add_key_arg {
     struct fscrypt_key_specifier key_spec;
     __u32 raw_size;
-    __u32 __reserved[8];
+    __u32 key_id;
+    __u32 __reserved[7];
     __u32 flags;
     __u8 raw[];
 };
 
+struct sys_fscrypt_provisioning_key_payload {
+    __u32 type;
+    __u32 __reserved;
+    __u8 raw[];
+};
+
 #define fscrypt_add_key_arg sys_fscrypt_add_key_arg
+#define fscrypt_provisioning_key_payload sys_fscrypt_provisioning_key_payload
 
 #endif  //_UAPI_LINUX_FSCRYPT_VOLD_H