commit 20e3960e245f6dfa57fa5c9124b0fd33e679f723
author Alex Deymo <deymo@google.com> Mon Apr 04 19:09:22 2016 -0700
committer Alex Deymo <deymo@google.com> Tue Apr 05 08:32:58 2016 -0700
tree 1e76cf3bc9913502f4a71a1fb6d0e810c963e8ac
parent 0d29854cf5bb05a22cf161b50052539aa420a36e

Make transition to "postinstall" domain explicit.

When running the postinstall program, we were relying on the automatic
transition between update_engine domain and postinstall, which required
postinstall_file to be an entrypoint for such domain. This patch makes
the transition explicit by calling setexeccon(3).

Bug: 28008031
TEST=make dist; Deployed an update to edison-eng: postinstall runs as "postinstall" domain.

Change-Id: I27d404886841e0bd39589f0274eaaf98929eeac9

common/subprocess.cc

diff --git a/common/subprocess.cc b/common/subprocess.cc
index 9738b1d..9473f10 100644
--- a/common/subprocess.cc
+++ b/common/subprocess.cc
@@ -32,6 +32,9 @@
 #include <base/strings/stringprintf.h>
 #include <brillo/process.h>
 #include <brillo/secure_blob.h>
+#ifdef __ANDROID__
+#include <selinux/selinux.h>
+#endif  // __ANDROID__
 
 #include "update_engine/common/utils.h"
 
@@ -44,7 +47,9 @@
 
 namespace {
 
-bool SetupChild(const std::map<string, string>& env, uint32_t flags) {
+bool SetupChild(const std::map<string, string>& env,
+                uint32_t flags,
+                const char* se_domain) {
   // Setup the environment variables.
   clearenv();
   for (const auto& key_value : env) {
@@ -63,6 +68,15 @@
     return false;
   IGNORE_EINTR(close(fd));
 
+#ifdef __ANDROID__
+  // setexeccon(3) accepts a nullptr to indicate the default context policy.
+  if (setexeccon(se_domain) < 0) {
+    PLOG(ERROR) << "Error setting the SELinux domain to "
+                << (se_domain ? se_domain : "<nullptr>");
+    return false;
+  }
+#endif  // __ANDROID__
+
   return true;
 }
 
@@ -74,6 +88,7 @@
 bool LaunchProcess(const vector<string>& cmd,
                    uint32_t flags,
                    const vector<int>& output_pipes,
+                   const char* se_domain,
                    brillo::Process* proc) {
   for (const string& arg : cmd)
     proc->AddArg(arg);
@@ -92,7 +107,7 @@
   }
   proc->SetCloseUnusedFileDescriptors(true);
   proc->RedirectUsingPipe(STDOUT_FILENO, false);
-  proc->SetPreExecCallback(base::Bind(&SetupChild, env, flags));
+  proc->SetPreExecCallback(base::Bind(&SetupChild, env, flags, se_domain));
 
   return proc->Start();
 }
@@ -170,16 +185,17 @@
 
 pid_t Subprocess::Exec(const vector<string>& cmd,
                        const ExecCallback& callback) {
-  return ExecFlags(cmd, kRedirectStderrToStdout, {}, callback);
+  return ExecFlags(cmd, kRedirectStderrToStdout, {}, nullptr, callback);
 }
 
 pid_t Subprocess::ExecFlags(const vector<string>& cmd,
                             uint32_t flags,
                             const vector<int>& output_pipes,
+                            const char* se_domain,
                             const ExecCallback& callback) {
   unique_ptr<SubprocessRecord> record(new SubprocessRecord(callback));
 
-  if (!LaunchProcess(cmd, flags, output_pipes, &record->proc)) {
+  if (!LaunchProcess(cmd, flags, output_pipes, se_domain, &record->proc)) {
     LOG(ERROR) << "Failed to launch subprocess";
     return 0;
   }
@@ -248,7 +264,7 @@
   // It doesn't make sense to redirect some pipes in the synchronous case
   // because we won't be reading on our end, so we don't expose the output_pipes
   // in this case.
-  if (!LaunchProcess(cmd, flags, {}, &proc)) {
+  if (!LaunchProcess(cmd, flags, {}, nullptr, &proc)) {
     LOG(ERROR) << "Failed to launch subprocess";
     return false;
   }

common/subprocess.h

diff --git a/common/subprocess.h b/common/subprocess.h
index b655fb7..6c99c8d 100644
--- a/common/subprocess.h
+++ b/common/subprocess.h
@@ -73,6 +73,7 @@
   pid_t ExecFlags(const std::vector<std::string>& cmd,
                   uint32_t flags,
                   const std::vector<int>& output_pipes,
+                  const char* se_domain,
                   const ExecCallback& callback);
 
   // Kills the running process with SIGTERM and ignores the callback.

common/subprocess_unittest.cc

diff --git a/common/subprocess_unittest.cc b/common/subprocess_unittest.cc
index 5ca44e8..d5e33bb 100644
--- a/common/subprocess_unittest.cc
+++ b/common/subprocess_unittest.cc
@@ -148,6 +148,7 @@
       {kBinPath "/sh", "-c", "echo on stdout; echo on stderr >&2"},
       0,
       {},
+      nullptr,
       base::Bind(&ExpectedResults, 0, "on stdout\n")));
   loop_.Run();
 }
@@ -158,6 +159,7 @@
       {kBinPath "/sh", "-c", "echo on pipe >&3"},
       0,
       {3},
+      nullptr,
       base::Bind(&ExpectedDataOnPipe, &subprocess_, &pid, 3, "on pipe\n", 0));
   EXPECT_NE(0, pid);
 
@@ -174,10 +176,7 @@
   const vector<string> cmd = {kBinPath "/sh", "-c",
      base::StringPrintf("echo on pipe >/proc/self/fd/%d", pipe.writer)};
   EXPECT_TRUE(subprocess_.ExecFlags(
-      cmd,
-      0,
-      {},
-      base::Bind(&ExpectedResults, 1, "")));
+      cmd, 0, {}, nullptr, base::Bind(&ExpectedResults, 1, "")));
   loop_.Run();
 }