Currently NaCl‘s Chromium integration does not work when combined with Chromium’s [Linux sandbox] ( (specifically, the SUID sandbox). Using NaCl under Chromium requires the options --internal-nacl --no-sandbox (e.g. see [this announcement] (


The following things need to be done to make this work:

  • Make the combination work without --no-sandbox. This means making the renderer process work.
    • Currently the plugin gives an assertion failure when it fails to open /dev/urandom, killing the renderer process. The fix is to open /dev/urandom before switching on sandboxing. - DONE
    • The SRPC plugin tries to open /dev/shm/XXX to use shared memory, which fails. The fix is to create shared memory segments using an RPC to an unsandboxed process. - DONE
  • Make sel_ldr run under the sandbox:
    • Ensure that standalone sel_ldr can work under the sandbox. Test this by running NaCl's test cases in this sandbox. (Some tests will work but others require filesystem access and will not work.)
    • Ensure that the sel_ldr side of the NaCl plugin works under the sandbox. Is there a way of testing this in isolation from the web browser?
    • Hook it up in Chromium so that sel_ldr is launched in the sandbox. - DONE

Seccomp sandbox

Running NaCl under the seccomp sandbox raises the following issues:

  • NaCl‘s internal IMC library uses Linux’s Unix domain socket “abstract namespace”. This involves creating sockets using socket(), bind() and connect(), which are blocked by the seccomp sandbox.
    • Immediate problem: NaClCommonDescMakeBoundSock() in nrd_xfer.c goes into an infinite loop because NaClBoundSocket() repeatedly fails.
    • We should probably abandon IMCSockets' concept of SocketAddress/BoundSockets having names. We can use Linux SOCK_SEQPACKET sockets for these endpoints instead; these will be unforgeable, not just unguessable.
  • x86's RDTSC instruction. See [this thread] (


The Linux SUID sandbox marks sandboxed processes as undumpable, which stops them from being ptrace()‘d. This appears to prevent the Breakpad crash reporting system from working, since Breakpad currently uses ptrace() to read processes’ state.