Linux sandbox: restrict clone() in renderer processes.

content/common/sandbox_seccomp_bpf_linux.cc

Index: content/common/sandbox_seccomp_bpf_linux.cc
diff --git a/content/common/sandbox_seccomp_bpf_linux.cc b/content/common/sandbox_seccomp_bpf_linux.cc
index 7051acb93a65132ee1048a72682e456d9bb06231..748f07edee27fb8bc315a5e752814d43d268e599 100644
--- a/content/common/sandbox_seccomp_bpf_linux.cc
+++ b/content/common/sandbox_seccomp_bpf_linux.cc
@@ -101,6 +101,24 @@ intptr_t CrashSIGSYS_Handler(const struct arch_seccomp_data& args, void* aux) {
     _exit(1);
 }
 
+// TODO(jln): rewrite reporting functions.
+intptr_t ReportCloneFailure(const struct arch_seccomp_data& args, void* aux) {
+  // "flags" in the first argument in the kernel's clone().
+  // Mark as volatile to be able to find the value on the stack in a minidump.
+#if !defined(NDEBUG)
+  RAW_LOG(ERROR, __FILE__":**CRASHING**:clone() failure\n");
+#endif
+  volatile uint64_t clone_flags = args.args[0];
+  volatile char* addr =
+      reinterpret_cast<volatile char*>(clone_flags & 0xFFFFFF);
+  *addr = '\0';
+  // Hit the NULL page if this fails to fault.
+  addr = reinterpret_cast<volatile char*>(clone_flags & 0xFFF);
+  *addr = '\0';
+  for (;;)
+    _exit(1);
+}
+
 bool IsAcceleratedVideoDecodeEnabled() {
   // Accelerated video decode is currently enabled on Chrome OS,
   // but not on Linux: crbug.com/137247.
@@ -1236,8 +1254,24 @@ ErrorCode GpuBrokerProcessPolicy(int sysno, void*) {
   }
 }
 
+// Allow clone for threads, crash if anything else is attempted.
+ErrorCode RestrictCloneToThreads() {
+  // Glibc's pthread.
+  return Sandbox::Cond(0, ErrorCode::TP_32BIT, ErrorCode::OP_EQUAL,
+                       CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND |
+                       CLONE_THREAD | CLONE_SYSVSEM | CLONE_SETTLS |
+                       CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID,
+                       ErrorCode(ErrorCode::ERR_ALLOWED),
+                       Sandbox::Trap(ReportCloneFailure, NULL));
+}
+
 ErrorCode RendererOrWorkerProcessPolicy(int sysno, void *) {
   switch (sysno) {
+    case __NR_clone:
+#if defined(__x86_64__) && defined(OS_LINUX)
+      // TODO(jln): extend to other architectures.
+      return RestrictCloneToThreads();
+#endif
     case __NR_ioctl:  // TODO(jln) investigate legitimate use in the renderer
                       // and see if alternatives can be used.
     case __NR_fdatasync: