Merge "installd: allow enabling fs-verity to a given file" into main am: 81b651b9e4 am: 9dc2e6bf9f

Original change: https://android-review.googlesource.com/c/platform/frameworks/native/+/2681476

Change-Id: I903ecba1d1de1dad0e41e86cadb240a2342c2384
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

4 files changed, 269 insertions, 0 deletions

diff --git a/cmds/installd/InstalldNativeService.cpp b/cmds/installd/InstalldNativeService.cpp
index b302f52f3e..e2a2927f2b 100644
--- a/cmds/installd/InstalldNativeService.cpp
+++ b/cmds/installd/InstalldNativeService.cpp
@@ -19,6 +19,7 @@
 #include <errno.h>
 #include <fts.h>
 #include <inttypes.h>
+#include <linux/fsverity.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -51,6 +52,7 @@
 #include <android-base/unique_fd.h>
 #include <cutils/ashmem.h>
 #include <cutils/fs.h>
+#include <cutils/misc.h>
 #include <cutils/properties.h>
 #include <cutils/sched_policy.h>
 #include <linux/quota.h>
@@ -84,6 +86,8 @@
 using android::base::ParseUint;
 using android::base::Split;
 using android::base::StringPrintf;
+using android::base::unique_fd;
+using android::os::ParcelFileDescriptor;
 using std::endl;
 
 namespace android {
@@ -229,6 +233,14 @@ binder::Status checkArgumentFileName(const std::string& path) {
     return ok();
 }
 
+binder::Status checkUidInAppRange(int32_t appUid) {
+    if (FIRST_APPLICATION_UID <= appUid && appUid <= LAST_APPLICATION_UID) {
+        return ok();
+    }
+    return exception(binder::Status::EX_ILLEGAL_ARGUMENT,
+                     StringPrintf("UID %d is outside of the range", appUid));
+}
+
 #define ENFORCE_UID(uid) {                                  \
     binder::Status status = checkUid((uid));                \
     if (!status.isOk()) {                                   \
@@ -283,6 +295,14 @@ binder::Status checkArgumentFileName(const std::string& path) {
         }                                                      \
     }
 
+#define CHECK_ARGUMENT_UID_IN_APP_RANGE(uid)               \
+    {                                                      \
+        binder::Status status = checkUidInAppRange((uid)); \
+        if (!status.isOk()) {                              \
+            return status;                                 \
+        }                                                  \
+    }
+
 #ifdef GRANULAR_LOCKS
 
 /**
@@ -383,6 +403,33 @@ using PackageLockGuard = std::lock_guard<PackageLock>;
 
 }  // namespace
 
+binder::Status InstalldNativeService::FsveritySetupAuthToken::authenticate(
+        const ParcelFileDescriptor& authFd, int32_t appUid, int32_t userId) {
+    int open_flags = fcntl(authFd.get(), F_GETFL);
+    if (open_flags < 0) {
+        return exception(binder::Status::EX_SERVICE_SPECIFIC, "fcntl failed");
+    }
+    if ((open_flags & O_ACCMODE) != O_WRONLY && (open_flags & O_ACCMODE) != O_RDWR) {
+        return exception(binder::Status::EX_SECURITY, "Received FD with unexpected open flag");
+    }
+    if (fstat(authFd.get(), &this->mStatFromAuthFd) < 0) {
+        return exception(binder::Status::EX_SERVICE_SPECIFIC, "fstat failed");
+    }
+    if (!S_ISREG(this->mStatFromAuthFd.st_mode)) {
+        return exception(binder::Status::EX_SECURITY, "Not a regular file");
+    }
+    // Don't accept a file owned by a different app.
+    uid_t uid = multiuser_get_uid(userId, appUid);
+    if (this->mStatFromAuthFd.st_uid != uid) {
+        return exception(binder::Status::EX_SERVICE_SPECIFIC, "File not owned by appUid");
+    }
+    return ok();
+}
+
+bool InstalldNativeService::FsveritySetupAuthToken::isSameStat(const struct stat& st) const {
+    return memcmp(&st, &mStatFromAuthFd, sizeof(st)) == 0;
+}
+
 status_t InstalldNativeService::start() {
     IPCThreadState::self()->disableBackgroundScheduling(true);
     status_t ret = BinderService<InstalldNativeService>::publish();
@@ -3857,5 +3904,84 @@ binder::Status InstalldNativeService::getOdexVisibility(
     return *_aidl_return == -1 ? error() : ok();
 }
 
+// Creates an auth token to be used in enableFsverity. This token is really to store a proof that
+// the caller can write to a file, represented by the authFd. Effectively, system_server as the
+// attacker-in-the-middle cannot enable fs-verity on arbitrary app files. If the FD is not writable,
+// return null.
+//
+// appUid and userId are passed for additional ownership check, such that one app can not be
+// authenticated for another app's file. These parameters are assumed trusted for this purpose of
+// consistency check.
+//
+// Notably, creating the token allows us to manage the writable FD easily during enableFsverity.
+// Since enabling fs-verity to a file requires no outstanding writable FD, passing the authFd to the
+// server allows the server to hold the only reference (as long as the client app doesn't).
+binder::Status InstalldNativeService::createFsveritySetupAuthToken(
+        const ParcelFileDescriptor& authFd, int32_t appUid, int32_t userId,
+        sp<IFsveritySetupAuthToken>* _aidl_return) {
+    CHECK_ARGUMENT_UID_IN_APP_RANGE(appUid);
+    ENFORCE_VALID_USER(userId);
+
+    auto token = sp<FsveritySetupAuthToken>::make();
+    binder::Status status = token->authenticate(authFd, appUid, userId);
+    if (!status.isOk()) {
+        return status;
+    }
+    *_aidl_return = token;
+    return ok();
+}
+
+// Enables fs-verity for filePath, which must be an absolute path and the same inode as in the auth
+// token previously returned from createFsveritySetupAuthToken, and owned by the app uid. As
+// installd is more privileged than its client / system server, we attempt to limit what a
+// (compromised) client can do.
+//
+// The reason for this app request to go through installd is to avoid exposing a risky area (PKCS#7
+// signature verification) in the kernel to the app as an attack surface (it can't be system server
+// because it can't override DAC and manipulate app files). Note that we should be able to drop
+// these hops and simply the app calls the ioctl, once all upgrading devices run with a kernel
+// without fs-verity built-in signature (https://r.android.com/2650402).
+binder::Status InstalldNativeService::enableFsverity(const sp<IFsveritySetupAuthToken>& authToken,
+                                                     const std::string& filePath,
+                                                     const std::string& packageName,
+                                                     int32_t* _aidl_return) {
+    ENFORCE_UID(AID_SYSTEM);
+    CHECK_ARGUMENT_PATH(filePath);
+    CHECK_ARGUMENT_PACKAGE_NAME(packageName);
+    LOCK_PACKAGE();
+    if (authToken == nullptr) {
+        return exception(binder::Status::EX_ILLEGAL_ARGUMENT, "Received a null auth token");
+    }
+
+    // Authenticate to check the targeting file is the same inode as the authFd.
+    sp<IBinder> authTokenBinder = IInterface::asBinder(authToken)->localBinder();
+    if (authTokenBinder == nullptr) {
+        return exception(binder::Status::EX_SECURITY, "Received a non-local auth token");
+    }
+    auto authTokenInstance = sp<FsveritySetupAuthToken>::cast(authTokenBinder);
+    unique_fd rfd(open(filePath.c_str(), O_RDONLY | O_CLOEXEC | O_NOFOLLOW));
+    struct stat stFromPath;
+    if (fstat(rfd.get(), &stFromPath) < 0) {
+        *_aidl_return = errno;
+        return ok();
+    }
+    if (!authTokenInstance->isSameStat(stFromPath)) {
+        LOG(DEBUG) << "FD authentication failed";
+        *_aidl_return = EPERM;
+        return ok();
+    }
+
+    fsverity_enable_arg arg = {};
+    arg.version = 1;
+    arg.hash_algorithm = FS_VERITY_HASH_ALG_SHA256;
+    arg.block_size = 4096;
+    if (ioctl(rfd.get(), FS_IOC_ENABLE_VERITY, &arg) < 0) {
+        *_aidl_return = errno;
+    } else {
+        *_aidl_return = 0;
+    }
+    return ok();
+}
+
 }  // namespace installd
 }  // namespace android
diff --git a/cmds/installd/InstalldNativeService.h b/cmds/installd/InstalldNativeService.h
index 521afc3f97..0f28234422 100644
--- a/cmds/installd/InstalldNativeService.h
+++ b/cmds/installd/InstalldNativeService.h
@@ -19,6 +19,7 @@
 #define COMMANDS_H_
 
 #include <inttypes.h>
+#include <sys/stat.h>
 #include <unistd.h>
 
 #include <shared_mutex>
@@ -35,8 +36,26 @@
 namespace android {
 namespace installd {
 
+using IFsveritySetupAuthToken = android::os::IInstalld::IFsveritySetupAuthToken;
+
 class InstalldNativeService : public BinderService<InstalldNativeService>, public os::BnInstalld {
 public:
+    class FsveritySetupAuthToken : public os::IInstalld::BnFsveritySetupAuthToken {
+    public:
+        FsveritySetupAuthToken() : mStatFromAuthFd() {}
+
+        binder::Status authenticate(const android::os::ParcelFileDescriptor& authFd, int32_t appUid,
+                                    int32_t userId);
+        bool isSameStat(const struct stat& st) const;
+
+    private:
+        // Not copyable or movable
+        FsveritySetupAuthToken(const FsveritySetupAuthToken&) = delete;
+        FsveritySetupAuthToken& operator=(const FsveritySetupAuthToken&) = delete;
+
+        struct stat mStatFromAuthFd;
+    };
+
     static status_t start();
     static char const* getServiceName() { return "installd"; }
     virtual status_t dump(int fd, const Vector<String16> &args) override;
@@ -192,6 +211,13 @@ public:
                                      const std::optional<std::string>& outputPath,
                                      int32_t* _aidl_return);
 
+    binder::Status createFsveritySetupAuthToken(const android::os::ParcelFileDescriptor& authFd,
+                                                int32_t appUid, int32_t userId,
+                                                android::sp<IFsveritySetupAuthToken>* _aidl_return);
+    binder::Status enableFsverity(const android::sp<IFsveritySetupAuthToken>& authToken,
+                                  const std::string& filePath, const std::string& packageName,
+                                  int32_t* _aidl_return);
+
 private:
     std::recursive_mutex mLock;
     std::unordered_map<userid_t, std::weak_ptr<std::shared_mutex>> mUserIdLock;
diff --git a/cmds/installd/binder/android/os/IInstalld.aidl b/cmds/installd/binder/android/os/IInstalld.aidl
index 9ad853b1df..8893e38c03 100644
--- a/cmds/installd/binder/android/os/IInstalld.aidl
+++ b/cmds/installd/binder/android/os/IInstalld.aidl
@@ -134,6 +134,22 @@ interface IInstalld {
     int getOdexVisibility(@utf8InCpp String packageName, @utf8InCpp String apkPath,
             @utf8InCpp String instructionSet, @nullable @utf8InCpp String outputPath);
 
+    interface IFsveritySetupAuthToken {
+        // Using an interface here is an easy way to create and maintain an IBinder object across
+        // the processes. When installd creates this binder object, it stores the file stat
+        // privately for later authentication, and only returns the reference to the caller process.
+        // Once the binder object has no reference count, it gets destructed automatically
+        // (alternatively, installd can maintain an internal mapping, but it is more error prone
+        // because the app may crash and not finish the fs-verity setup, keeping the memory unused
+        // forever).
+        //
+        // We don't necessarily need a method here, so it's left blank intentionally.
+    }
+    IFsveritySetupAuthToken createFsveritySetupAuthToken(in ParcelFileDescriptor authFd, int appUid,
+            int userId);
+    int enableFsverity(in IFsveritySetupAuthToken authToken, @utf8InCpp String filePath,
+            @utf8InCpp String packageName);
+
     const int FLAG_STORAGE_DE = 0x1;
     const int FLAG_STORAGE_CE = 0x2;
     const int FLAG_STORAGE_EXTERNAL = 0x4;
diff --git a/cmds/installd/tests/installd_service_test.cpp b/cmds/installd/tests/installd_service_test.cpp
index 858a92cc65..4bc92afa18 100644
--- a/cmds/installd/tests/installd_service_test.cpp
+++ b/cmds/installd/tests/installd_service_test.cpp
@@ -42,9 +42,12 @@
 #include "binder_test_utils.h"
 #include "dexopt.h"
 #include "globals.h"
+#include "unique_file.h"
 #include "utils.h"
 
 using android::base::StringPrintf;
+using android::base::unique_fd;
+using android::os::ParcelFileDescriptor;
 using std::filesystem::is_empty;
 
 namespace android {
@@ -136,6 +139,16 @@ static int create(const std::string& path, uid_t owner, gid_t group, mode_t mode
     return fd;
 }
 
+static void create_with_content(const std::string& path, uid_t owner, gid_t group, mode_t mode,
+                                const std::string& content) {
+    int fd = ::open(path.c_str(), O_RDWR | O_CREAT, mode);
+    EXPECT_NE(fd, -1);
+    EXPECT_TRUE(android::base::WriteStringToFd(content, fd));
+    EXPECT_EQ(::fchown(fd, owner, group), 0);
+    EXPECT_EQ(::fchmod(fd, mode), 0);
+    close(fd);
+}
+
 static void touch(const std::string& path, uid_t owner, gid_t group, mode_t mode) {
     EXPECT_EQ(::close(create(path.c_str(), owner, group, mode)), 0);
 }
@@ -527,6 +540,94 @@ TEST_F(ServiceTest, GetAppSizeWrongSizes) {
                                            externalStorageAppId, ceDataInodes, codePaths,
                                            &externalStorageSize));
 }
+
+class FsverityTest : public ServiceTest {
+protected:
+    binder::Status createFsveritySetupAuthToken(const std::string& path, int open_mode,
+                                                sp<IFsveritySetupAuthToken>* _aidl_return) {
+        unique_fd ufd(open(path.c_str(), open_mode));
+        EXPECT_GE(ufd.get(), 0) << "open failed: " << strerror(errno);
+        ParcelFileDescriptor rfd(std::move(ufd));
+        return service->createFsveritySetupAuthToken(std::move(rfd), kTestAppId, kTestUserId,
+                                                     _aidl_return);
+    }
+};
+
+TEST_F(FsverityTest, enableFsverity) {
+    const std::string path = kTestPath + "/foo";
+    create_with_content(path, kTestAppUid, kTestAppUid, 0600, "content");
+    UniqueFile raii(/*fd=*/-1, path, [](const std::string& path) { unlink(path.c_str()); });
+
+    // Expect to fs-verity setup to succeed
+    sp<IFsveritySetupAuthToken> authToken;
+    binder::Status status = createFsveritySetupAuthToken(path, O_RDWR, &authToken);
+    EXPECT_TRUE(status.isOk());
+    EXPECT_TRUE(authToken != nullptr);
+
+    // Verity auth token works to enable fs-verity
+    int32_t errno_local;
+    status = service->enableFsverity(authToken, path, "fake.package.name", &errno_local);
+    EXPECT_TRUE(status.isOk());
+    EXPECT_EQ(errno_local, 0);
+}
+
+TEST_F(FsverityTest, enableFsverity_nullAuthToken) {
+    const std::string path = kTestPath + "/foo";
+    create_with_content(path, kTestAppUid, kTestAppUid, 0600, "content");
+    UniqueFile raii(/*fd=*/-1, path, [](const std::string& path) { unlink(path.c_str()); });
+
+    // Verity null auth token fails
+    sp<IFsveritySetupAuthToken> authToken;
+    int32_t errno_local;
+    binder::Status status =
+            service->enableFsverity(authToken, path, "fake.package.name", &errno_local);
+    EXPECT_FALSE(status.isOk());
+}
+
+TEST_F(FsverityTest, enableFsverity_differentFile) {
+    const std::string path = kTestPath + "/foo";
+    create_with_content(path, kTestAppUid, kTestAppUid, 0600, "content");
+    UniqueFile raii(/*fd=*/-1, path, [](const std::string& path) { unlink(path.c_str()); });
+
+    // Expect to fs-verity setup to succeed
+    sp<IFsveritySetupAuthToken> authToken;
+    binder::Status status = createFsveritySetupAuthToken(path, O_RDWR, &authToken);
+    EXPECT_TRUE(status.isOk());
+    EXPECT_TRUE(authToken != nullptr);
+
+    // Verity auth token does not work for a different file
+    const std::string anotherPath = kTestPath + "/bar";
+    ASSERT_TRUE(android::base::WriteStringToFile("content", anotherPath));
+    UniqueFile raii2(/*fd=*/-1, anotherPath, [](const std::string& path) { unlink(path.c_str()); });
+    int32_t errno_local;
+    status = service->enableFsverity(authToken, anotherPath, "fake.package.name", &errno_local);
+    EXPECT_TRUE(status.isOk());
+    EXPECT_NE(errno_local, 0);
+}
+
+TEST_F(FsverityTest, createFsveritySetupAuthToken_ReadonlyFdDoesNotAuthenticate) {
+    const std::string path = kTestPath + "/foo";
+    create_with_content(path, kTestAppUid, kTestAppUid, 0600, "content");
+    UniqueFile raii(/*fd=*/-1, path, [](const std::string& path) { unlink(path.c_str()); });
+
+    // Expect the fs-verity setup to fail
+    sp<IFsveritySetupAuthToken> authToken;
+    binder::Status status = createFsveritySetupAuthToken(path, O_RDONLY, &authToken);
+    EXPECT_FALSE(status.isOk());
+}
+
+TEST_F(FsverityTest, createFsveritySetupAuthToken_UnownedFile) {
+    const std::string path = kTestPath + "/foo";
+    // Simulate world-writable file owned by another app
+    create_with_content(path, kTestAppUid + 1, kTestAppUid + 1, 0666, "content");
+    UniqueFile raii(/*fd=*/-1, path, [](const std::string& path) { unlink(path.c_str()); });
+
+    // Expect the fs-verity setup to fail
+    sp<IFsveritySetupAuthToken> authToken;
+    binder::Status status = createFsveritySetupAuthToken(path, O_RDWR, &authToken);
+    EXPECT_FALSE(status.isOk());
+}
+
 static bool mkdirs(const std::string& path, mode_t mode) {
     struct stat sb;
     if (stat(path.c_str(), &sb) != -1 && S_ISDIR(sb.st_mode)) {