[Android] Allow __NR_rt_tgsigqueueinfo under seccomp.

content/common/sandbox_linux/android/sandbox_bpf_base_policy_android.cc

Index: content/common/sandbox_linux/android/sandbox_bpf_base_policy_android.cc
diff --git a/content/common/sandbox_linux/android/sandbox_bpf_base_policy_android.cc b/content/common/sandbox_linux/android/sandbox_bpf_base_policy_android.cc
index 4cd502d8487729950a891e6fc610a0bb946c35c5..110232b2b602a33dd98365bc243defd72cc00cbe 100644
--- a/content/common/sandbox_linux/android/sandbox_bpf_base_policy_android.cc
+++ b/content/common/sandbox_linux/android/sandbox_bpf_base_policy_android.cc
@@ -122,6 +122,13 @@ ResultExpr SandboxBPFBasePolicyAndroid::EvaluateSyscall(int sysno) const {
       break;
   }
 
+  // https://crbug.com/644759
+  if (sysno == __NR_rt_tgsigqueueinfo) {
+    const Arg<pid_t> tgid(0);
+    return If(tgid == getpid(), Allow())

[jln (very slow on Chromium), 2016/09/07 23:22:05]

Do you want to just capture the current pid as a member variable of the policy
(see policy_pid_ in baseline_policy.h). It's good practice to make the condition
of If() as "constant" as possible.

Note: the uinfo argument of this syscall sadly allows to spoof the sender PIDs,
which has been a security issue in the past. Fixing this with seccomp is very
convoluted, so I don't think we want to go there.
(I fixed it in Linux in
http://www.openwall.com/lists/oss-security/2011/03/22/13, but it regressed
later).

[Robert Sesek, 2016/09/08 18:33:02]

Done.
That is unfortunate. However I think the risk is minimal here, given that we at
worst we would signal ourselves.

+           .Else(Error(EPERM));
+  }
+
 #if defined(__x86_64__) || defined(__arm__) || defined(__aarch64__) || \
       defined(__mips__)
   if (sysno == __NR_socket) {