mediaex: apply seccomp filter
We can safely reduce the number of accessible system calls from ~250
down to ~30.
This commit adds a seccomp filter for arm/arm64 devices. Mediaextractor
runs as a 32 bit process so the same filter is used for both arm and
arm64 devices. The filter is arranged by frequency of the systemcall to
provide the best performance.
Most system calls are whitelisted without argument inspection. The
exception is the socket syscall where the first argument is checked to
ensure only domain=AF_LOCAL sockets are allowed - used for logging.
Vendor additions may be appended to the default filter by creating
mediaextractor-seccomp.policy file and pointing BOARD_SECCOMP_POLICY
to the directory where it resides. For example:
create: device/<oem>/<target>/seccomp/mediaextractor-seccomp.policy
with the necessary syscalls. set:
BOARD_SECCOMP_POLICY=device/<oem>/<target>/seccomp
in the device's BoardConfig.mk
Change-Id: I384a43beaa18f10081c15320a795d9d9d0180de4
diff --git a/services/mediaextractor/minijail/minijail.cpp b/services/mediaextractor/minijail/minijail.cpp
new file mode 100644
index 0000000..421a1e0
--- /dev/null
+++ b/services/mediaextractor/minijail/minijail.cpp
@@ -0,0 +1,50 @@
+/*
+**
+** Copyright 2015, The Android Open Source Project
+**
+** Licensed under the Apache License, Version 2.0 (the "License");
+** you may not use this file except in compliance with the License.
+** You may obtain a copy of the License at
+**
+** http://www.apache.org/licenses/LICENSE-2.0
+**
+** Unless required by applicable law or agreed to in writing, software
+** distributed under the License is distributed on an "AS IS" BASIS,
+** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+** See the License for the specific language governing permissions and
+** limitations under the License.
+*/
+
+#include <cutils/log.h>
+#include <libminijail.h>
+
+#include "minijail.h"
+
+namespace android {
+
+/* Must match location in Android.mk */
+static const char kSeccompFilePath[] = "/system/etc/seccomp_policy/mediaextractor-seccomp.policy";
+
+int MiniJail()
+{
+ /* no seccomp policy for this architecture */
+ if (access(kSeccompFilePath, R_OK) == -1) {
+ ALOGW("No seccomp filter defined for this architecture.");
+ return 0;
+ }
+
+ struct minijail *jail = minijail_new();
+ if (jail == NULL) {
+ ALOGW("Failed to create minijail.");
+ return -1;
+ }
+
+ minijail_no_new_privs(jail);
+ minijail_log_seccomp_filter_failures(jail);
+ minijail_use_seccomp_filter(jail);
+ minijail_parse_seccomp_filters(jail, kSeccompFilePath);
+ minijail_enter(jail);
+ minijail_destroy(jail);
+ return 0;
+}
+}