Linux, Android: fix call to setpriority(2).

setpriority(), when used with PRIO_PROCESS, should affect the whole
process (i.e. thread group). On Linux the system call only affects one
thread (this bug is documented in
http://man7.org/linux/man-pages/man2/getpriority.2.html) and thus lets
the caller specify a tid.

This CL changes the call to setpriority(PRIO_PROCESS, tid, ...) to
setpriority(PRIO_PROCESS, 0, ...), which is strictly equivalent, albeit
slightly more correct.

This makes filtering system calls in our sandbox easier, as the current thread
id is not known to the BPF filter.

BUG=399473
R=mdempsky@chromium.org, willchan@chromium.org

Review URL: https://codereview.chromium.org/434803003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286964 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 24 insertions, 13 deletions

diff --git a/base/threading/platform_thread_android.cc b/base/threading/platform_thread_android.cc
index bd0b4b3..f8395e5 100644
--- a/base/threading/platform_thread_android.cc
+++ b/base/threading/platform_thread_android.cc
@@ -65,14 +65,20 @@ void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
     return;
   }
 
-  // setpriority(2) will set a thread's priority if it is passed a tid as
-  // the 'process identifier', not affecting the rest of the threads in the
-  // process. Setting this priority will only succeed if the user has been
-  // granted permission to adjust nice values on the system.
+  // setpriority(2) should change the whole thread group's (i.e. process)
+  // priority. however, on linux it will only change the target thread's
+  // priority. see the bugs section in
+  // http://man7.org/linux/man-pages/man2/getpriority.2.html.
+  // we prefer using 0 rather than the current thread id since they are
+  // equivalent but it makes sandboxing easier (https://crbug.com/399473).
   DCHECK_NE(handle.id_, kInvalidThreadId);
   int kNiceSetting = ThreadNiceValue(priority);
-  if (setpriority(PRIO_PROCESS, handle.id_, kNiceSetting))
+  const PlatformThreadId current_id = PlatformThread::CurrentId();
+  if (setpriority(PRIO_PROCESS,
+                  handle.id_ == current_id ? 0 : handle.id_,
+                  kNiceSetting)) {
     LOG(ERROR) << "Failed to set nice value of thread to " << kNiceSetting;
+  }
 }
 
 void PlatformThread::SetName(const char* name) {
diff --git a/base/threading/platform_thread_linux.cc b/base/threading/platform_thread_linux.cc
index 636e133..97e0932 100644
--- a/base/threading/platform_thread_linux.cc
+++ b/base/threading/platform_thread_linux.cc
@@ -75,22 +75,27 @@ void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
                                        ThreadPriority priority) {
 #if !defined(OS_NACL)
   if (priority == kThreadPriority_RealtimeAudio) {
-    const struct sched_param kRealTimePrio = { 8 };
+    const struct sched_param kRealTimePrio = {8};
     if (pthread_setschedparam(pthread_self(), SCHED_RR, &kRealTimePrio) == 0) {
       // Got real time priority, no need to set nice level.
       return;
     }
   }
 
-  // setpriority(2) will set a thread's priority if it is passed a tid as
-  // the 'process identifier', not affecting the rest of the threads in the
-  // process. Setting this priority will only succeed if the user has been
-  // granted permission to adjust nice values on the system.
+  // setpriority(2) should change the whole thread group's (i.e. process)
+  // priority. however, on linux it will only change the target thread's
+  // priority. see the bugs section in
+  // http://man7.org/linux/man-pages/man2/getpriority.2.html.
+  // we prefer using 0 rather than the current thread id since they are
+  // equivalent but it makes sandboxing easier (https://crbug.com/399473).
   DCHECK_NE(handle.id_, kInvalidThreadId);
   const int kNiceSetting = ThreadNiceValue(priority);
-  if (setpriority(PRIO_PROCESS, handle.id_, kNiceSetting)) {
-    DVPLOG(1) << "Failed to set nice value of thread ("
-              << handle.id_ << ") to " << kNiceSetting;
+  const PlatformThreadId current_id = PlatformThread::CurrentId();
+  if (setpriority(PRIO_PROCESS,
+                  handle.id_ == current_id ? 0 : handle.id_,
+                  kNiceSetting)) {
+    DVPLOG(1) << "Failed to set nice value of thread (" << handle.id_ << ") to "
+              << kNiceSetting;
   }
 #endif  //  !defined(OS_NACL)
 }