Revert "vold: remove session keyring workaround for old kernels"

Reason for revert: Still needed for <4.14 devices.

This reverts commit 0e87a83cba.

Change-Id: I025911c9cb033d8021e6f23c005ce546411b1472

Android.bp

@@ -62,6 +62,7 @@ cc_defaults {
         "libincfs",
         "libhidlbase",
         "libkeymint_support",
+        "libkeyutils",
         "liblog",
         "liblogwrap",
         "libselinux",

FsCrypt.cpp

@@ -48,6 +48,7 @@
 #include <cutils/properties.h>
 
 #include <fscrypt/fscrypt.h>
+#include <keyutils.h>
 #include <libdm/dm.h>
 
 #include <android-base/file.h>
@@ -73,6 +74,7 @@ using android::vold::retrieveOrGenerateKey;
 using android::vold::SetDefaultAcl;
 using android::vold::SetQuotaInherit;
 using android::vold::SetQuotaProjectId;
+using android::vold::writeStringToFile;
 using namespace android::fscrypt;
 using namespace android::dm;
 
@@ -636,6 +638,27 @@ bool fscrypt_create_user_keys(userid_t user_id, bool ephemeral) {
     return true;
 }
 
+// "Lock" all encrypted directories whose key has been removed.  This is needed
+// in the case where the keys are being put in the session keyring (rather in
+// the newer filesystem-level keyrings), because removing a key from the session
+// keyring doesn't affect inodes in the kernel's inode cache whose per-file key
+// was already set up.  So to remove the per-file keys and make the files
+// "appear encrypted", these inodes must be evicted.
+//
+// To do this, sync() to clean all dirty inodes, then drop all reclaimable slab
+// objects systemwide.  This is overkill, but it's the best available method
+// currently.  Don't use drop_caches mode "3" because that also evicts pagecache
+// for in-use files; all files relevant here are already closed and sync'ed.
+static void drop_caches_if_needed() {
+    if (android::vold::isFsKeyringSupported()) {
+        return;
+    }
+    sync();
+    if (!writeStringToFile("2", "/proc/sys/vm/drop_caches")) {
+        PLOG(ERROR) << "Failed to drop caches during key eviction";
+    }
+}
+
 // Evicts all the user's keys of one type from all volumes (internal and adoptable).
 // This evicts either CE keys or DE keys, depending on which map is passed.
 static bool evict_user_keys(std::map<userid_t, UserPolicies>& policy_map, userid_t user_id) {
@@ -648,6 +671,7 @@ static bool evict_user_keys(std::map<userid_t, UserPolicies>& policy_map, userid
             success &= android::vold::evictKey(BuildDataPath(volume_uuid), policy);
         }
         policy_map.erase(it);
+        drop_caches_if_needed();
     }
     return success;
 }

KeyUtil.cpp

@@ -28,6 +28,7 @@
 
 #include <android-base/file.h>
 #include <android-base/logging.h>
+#include <keyutils.h>
 
 #include "KeyStorage.h"
 #include "Utils.h"
@@ -74,6 +75,39 @@ bool generateStorageKey(const KeyGeneration& gen, KeyBuffer* key) {
     }
 }
 
+static bool isFsKeyringSupportedImpl() {
+    android::base::unique_fd fd(open("/data", O_RDONLY | O_DIRECTORY | O_CLOEXEC));
+
+    // FS_IOC_ADD_ENCRYPTION_KEY with a NULL argument will fail with ENOTTY if
+    // the ioctl isn't supported.  Otherwise it will fail with another error
+    // code such as EFAULT.
+    //
+    // Note that there's no need to check for FS_IOC_REMOVE_ENCRYPTION_KEY,
+    // since it's guaranteed to be available if FS_IOC_ADD_ENCRYPTION_KEY is.
+    // There's also no need to check for support on external volumes separately
+    // from /data, since either the kernel supports the ioctls on all
+    // fscrypt-capable filesystems or it doesn't.
+    errno = 0;
+    (void)ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, NULL);
+    if (errno == ENOTTY) {
+        LOG(INFO) << "Kernel doesn't support FS_IOC_ADD_ENCRYPTION_KEY.  Falling back to "
+                     "session keyring";
+        return false;
+    }
+    if (errno != EFAULT) {
+        PLOG(WARNING) << "Unexpected error from FS_IOC_ADD_ENCRYPTION_KEY";
+    }
+    LOG(DEBUG) << "Detected support for FS_IOC_ADD_ENCRYPTION_KEY";
+    return true;
+}
+
+// Return true if the kernel supports the ioctls to add/remove fscrypt keys
+// directly to/from the filesystem.
+bool isFsKeyringSupported(void) {
+    static bool supported = isFsKeyringSupportedImpl();
+    return supported;
+}
+
 // Get raw keyref - used to make keyname and to pass to ioctl
 static std::string generateKeyRef(const uint8_t* key, int length) {
     SHA512_CTX c;
@@ -93,6 +127,20 @@ static std::string generateKeyRef(const uint8_t* key, int length) {
     return std::string((char*)key_ref2, FSCRYPT_KEY_DESCRIPTOR_SIZE);
 }
 
+static bool fillKey(const KeyBuffer& key, fscrypt_key* fs_key) {
+    if (key.size() != FSCRYPT_MAX_KEY_SIZE) {
+        LOG(ERROR) << "Wrong size key " << key.size();
+        return false;
+    }
+    static_assert(FSCRYPT_MAX_KEY_SIZE == sizeof(fs_key->raw), "Mismatch of max key sizes");
+    fs_key->mode = 0;  // unused by kernel
+    memcpy(fs_key->raw, key.data(), key.size());
+    fs_key->size = key.size();
+    return true;
+}
+
+static char const* const NAME_PREFIXES[] = {"ext4", "f2fs", "fscrypt", nullptr};
+
 static std::string keyrefstring(const std::string& raw_ref) {
     std::ostringstream o;
     for (unsigned char i : raw_ref) {
@@ -101,6 +149,44 @@ static std::string keyrefstring(const std::string& raw_ref) {
     return o.str();
 }
 
+static std::string buildLegacyKeyName(const std::string& prefix, const std::string& raw_ref) {
+    return prefix + ":" + keyrefstring(raw_ref);
+}
+
+// Get the ID of the keyring we store all fscrypt keys in when the kernel is too
+// old to support FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY.
+static bool fscryptKeyring(key_serial_t* device_keyring) {
+    *device_keyring = keyctl_search(KEY_SPEC_SESSION_KEYRING, "keyring", "fscrypt", 0);
+    if (*device_keyring == -1) {
+        PLOG(ERROR) << "Unable to find device keyring";
+        return false;
+    }
+    return true;
+}
+
+// Add an encryption key to the legacy 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));
+    fscrypt_key& fs_key = *reinterpret_cast<fscrypt_key*>(fsKeyBuffer.data());
+
+    if (!fillKey(key, &fs_key)) return false;
+    key_serial_t device_keyring;
+    if (!fscryptKeyring(&device_keyring)) return false;
+    for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
+        auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
+        key_serial_t key_id =
+            add_key("logon", ref.c_str(), (void*)&fs_key, sizeof(fs_key), device_keyring);
+        if (key_id == -1) {
+            PLOG(ERROR) << "Failed to insert key into keyring " << device_keyring;
+            return false;
+        }
+        LOG(DEBUG) << "Added key " << key_id << " (" << ref << ") to keyring " << device_keyring
+                   << " in process " << getpid();
+    }
+    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) {
@@ -197,6 +283,29 @@ bool installKey(const std::string& mountpoint, const EncryptionOptions& options,
     return true;
 }
 
+// Remove an encryption key from the legacy global session keyring.
+static bool evictKeyLegacy(const std::string& raw_ref) {
+    key_serial_t device_keyring;
+    if (!fscryptKeyring(&device_keyring)) return false;
+    bool success = true;
+    for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
+        auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
+        auto key_serial = keyctl_search(device_keyring, "logon", ref.c_str(), 0);
+
+        // Unlink the key from the keyring.  Prefer unlinking to revoking or
+        // invalidating, since unlinking is actually no less secure currently, and
+        // it avoids bugs in certain kernel versions where the keyring key is
+        // referenced from places it shouldn't be.
+        if (keyctl_unlink(key_serial, device_keyring) != 0) {
+            PLOG(ERROR) << "Failed to unlink key with serial " << key_serial << " ref " << ref;
+            success = false;
+        } else {
+            LOG(DEBUG) << "Unlinked key with serial " << key_serial << " ref " << ref;
+        }
+    }
+    return success;
+}
+
 static void waitForBusyFiles(const struct fscrypt_key_specifier key_spec, const std::string ref,
                              const std::string mountpoint) {
     android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
@@ -257,6 +366,9 @@ static void waitForBusyFiles(const struct fscrypt_key_specifier key_spec, const
 
 bool evictKey(const std::string& mountpoint, const EncryptionPolicy& policy) {
     const std::lock_guard<std::mutex> lock(fscrypt_keyring_mutex);
+    if (policy.options.version == 1 && !isFsKeyringSupported()) {
+        return evictKeyLegacy(policy.key_raw_ref);
+    }
 
     android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
     if (fd == -1) {

KeyUtil.h

@@ -43,15 +43,28 @@ bool generateStorageKey(const KeyGeneration& gen, KeyBuffer* key);
 // be generated.
 const KeyGeneration neverGen();
 
+bool isFsKeyringSupported(void);
+
 // Install a file-based encryption key to the kernel, for use by encrypted files
 // 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.
+//
+// For v2 policies, we always use FS_IOC_ADD_ENCRYPTION_KEY; it's the only way
+// the kernel supports.
+//
 // 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 android::fscrypt::EncryptionOptions& options,
                 const KeyBuffer& key, android::fscrypt::EncryptionPolicy* policy);
 
 // Evict a file-based encryption key from the kernel.
+//
+// We use FS_IOC_REMOVE_ENCRYPTION_KEY if the kernel supports it.  Otherwise we
+// remove the key from the legacy global session keyring.
+//
+// In the latter case, the caller is responsible for dropping caches.
 bool evictKey(const std::string& mountpoint, const android::fscrypt::EncryptionPolicy& policy);
 
 // Retrieves the key from the named directory, or generates it if it doesn't