Android sandbox: workaround for restricted errno values.

sandbox/linux/seccomp-bpf/sandbox_bpf_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <errno.h>
 #include <pthread.h>
 #include <sched.h>
 #include <sys/prctl.h>
 #include <sys/syscall.h>
 #include <sys/time.h>
+#include <sys/types.h>
 #include <sys/utsname.h>
+#include <unistd.h>
 
 #if defined(ANDROID)
 // Work-around for buggy headers in Android's NDK
 #define __user
 #endif
 #include <linux/futex.h>
 
 #include <ostream>
 
 #include "base/memory/scoped_ptr.h"
+#include "build/build_config.h"
 #include "sandbox/linux/seccomp-bpf/bpf_tests.h"
 #include "sandbox/linux/seccomp-bpf/syscall.h"
 #include "sandbox/linux/seccomp-bpf/trap.h"
 #include "sandbox/linux/seccomp-bpf/verifier.h"
 #include "sandbox/linux/services/broker_process.h"
 #include "sandbox/linux/services/linux_syscalls.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 // Workaround for Android's prctl.h file.
 #ifndef PR_GET_ENDIAN
 #define PR_GET_ENDIAN   19
 #endif
 #ifndef PR_CAPBSET_READ
 #define PR_CAPBSET_READ 23
 #define PR_CAPBSET_DROP 24
 #endif
 
 using namespace playground2;
 using sandbox::BrokerProcess;
 
 namespace {
 
 const int  kExpectedReturnValue   = 42;
 const char kSandboxDebuggingEnv[] = "CHROME_SANDBOX_DEBUGGING";
 
+inline bool IsAndroid() {
+#if defined(OS_ANDROID)
+  return true;
+#else
+  return false;
+#endif
+}
+
 // This test should execute no matter whether we have kernel support. So,
 // we make it a TEST() instead of a BPF_TEST().
 TEST(SandboxBpf, CallSupports) {
   // We check that we don't crash, but it's ok if the kernel doesn't
   // support it.
   bool seccomp_bpf_supported =
       Sandbox::SupportsSeccompSandbox(-1) == Sandbox::STATUS_AVAILABLE;
   // We want to log whether or not seccomp BPF is actually supported
   // since actual test coverage depends on it.
   RecordProperty("SeccompBPFSupported",
@@ skipping 150 matching lines @@
   }
 
   switch (sysno) {
   case __NR_dup2:
     // Pretend that dup2() worked, but don't actually do anything.
     return ErrorCode(0);
   case __NR_setuid:
 #if defined(__NR_setuid32)
   case __NR_setuid32:
 #endif
-    // Return errno = 1
+    // Return errno = 1.
     return ErrorCode(1);
   case __NR_setgid:
 #if defined(__NR_setgid32)
   case __NR_setgid32:
 #endif
     // Return maximum errno value (typically 4095).
     return ErrorCode(ErrorCode::ERR_MAX_ERRNO);
+  case __NR_uname:
+    // Return errno = 42;
+    return ErrorCode(42);
   default:
     return ErrorCode(ErrorCode::ERR_ALLOWED);
   }
 }
 
 BPF_TEST(SandboxBpf, ErrnoTest, ErrnoTestPolicy) {
   // Verify that dup2() returns success, but doesn't actually run.
   int fds[4];
   BPF_ASSERT(pipe(fds) == 0);
   BPF_ASSERT(pipe(fds+2) == 0);
   BPF_ASSERT(dup2(fds[2], fds[0]) == 0);
   char buf[1] = { };
   BPF_ASSERT(write(fds[1], "\x55", 1) == 1);
   BPF_ASSERT(write(fds[3], "\xAA", 1) == 1);
   BPF_ASSERT(read(fds[0], buf, 1) == 1);
 
   // If dup2() executed, we will read \xAA, but it dup2() has been turned
   // into a no-op by our policy, then we will read \x55.
   BPF_ASSERT(buf[0] == '\x55');
 
   // Verify that we can return the minimum and maximum errno values.
+  errno = 0;
   BPF_ASSERT(setuid(0) == -1);
   BPF_ASSERT(errno == 1);
-  BPF_ASSERT(setgid(0) == -1);
-  BPF_ASSERT(errno == ErrorCode::ERR_MAX_ERRNO);
+
+  // On Android, errno is only supported up to 255, otherwise errno
+  // processing is skipped.
+  // We work around this (crbug.com/181647).
+  if (IsAndroid() && setgid(0) != -1) {
+    errno = 0;
+    BPF_ASSERT(setgid(0) == -ErrorCode::ERR_MAX_ERRNO);
+    BPF_ASSERT(errno == 0);
+  } else {
+    errno = 0;
+    BPF_ASSERT(setgid(0) == -1);
+    BPF_ASSERT(errno == ErrorCode::ERR_MAX_ERRNO);
+  }
+
+  // Finally, test an errno in between the minimum and maximum.
+  errno = 0;
+  struct utsname uts_buf;
+  BPF_ASSERT(uname(&uts_buf) == -1);
+  BPF_ASSERT(errno == 42);
 }
 
 // Testing the stacking of two sandboxes
 
 ErrorCode StackingPolicyPartOne(Sandbox *sandbox, int sysno, void *) {
   if (!Sandbox::IsValidSyscallNumber(sysno)) {
     return ErrorCode(ENOSYS);
   }
 
   switch (sysno) {
@@ skipping 1421 matching lines @@
 
 BPF_TEST(SandboxBpf, PthreadEquality, PthreadPolicyEquality) {
   PthreadTest();
 }
 
 BPF_TEST(SandboxBpf, PthreadBitMask, PthreadPolicyBitMask) {
   PthreadTest();
 }
 
 } // namespace