Pass the correct user ID to SetProcessProfilesCached()

SetProcessProfilesCached() can only set cgroup attributes in the v2
cgroup hierarchy if it is passed the correct user ID. Hence this CL.
This CL makes SetProcessProfilesCached() apply IO controller cgroup
attributes for processes with a user ID that is not zero.

Bug: 320456702
Bug: 213617178
Signed-off-by: Bart Van Assche <bvanassche@google.com>
(cherry picked from https://android-review.googlesource.com/q/commit:a615a850ee820848b2d464973855148e55c8c92f)
Merged-In: I84d072c14ff01422560c241a69cb9f4e02c47e74
Change-Id: I84d072c14ff01422560c241a69cb9f4e02c47e74

1 files changed, 32 insertions, 1 deletions

diff --git a/core/jni/android_util_Process.cpp b/core/jni/android_util_Process.cpp
index 91dfc6023e42..04b26b36fe63 100644
--- a/core/jni/android_util_Process.cpp
+++ b/core/jni/android_util_Process.cpp
@@ -28,6 +28,7 @@
 #include <meminfo/sysmeminfo.h>
 #include <processgroup/processgroup.h>
 #include <processgroup/sched_policy.h>
+#include <android-base/logging.h>
 #include <android-base/unique_fd.h>
 
 #include <algorithm>
@@ -232,6 +233,31 @@ void android_os_Process_setThreadGroupAndCpuset(JNIEnv* env, jobject clazz, int
     }
 }
 
+// Look up the user ID of a process in /proc/${pid}/status. The Uid: line is present in
+// /proc/${pid}/status since at least kernel v2.5.
+static int uid_from_pid(int pid)
+{
+    int uid = -1;
+    std::array<char, 64> path;
+    int res = snprintf(path.data(), path.size(), "/proc/%d/status", pid);
+    if (res < 0 || res >= static_cast<int>(path.size())) {
+        DCHECK(false);
+        return uid;
+    }
+    FILE* f = fopen(path.data(), "r");
+    if (!f) {
+        return uid;
+    }
+    char line[256];
+    while (fgets(line, sizeof(line), f)) {
+        if (sscanf(line, "Uid: %d", &uid) == 1) {
+            break;
+        }
+    }
+    fclose(f);
+    return uid;
+}
+
 void android_os_Process_setProcessGroup(JNIEnv* env, jobject clazz, int pid, jint grp)
 {
     ALOGV("%s pid=%d grp=%" PRId32, __func__, pid, grp);
@@ -275,7 +301,12 @@ void android_os_Process_setProcessGroup(JNIEnv* env, jobject clazz, int pid, jin
         }
     }
 
-    if (!SetProcessProfilesCached(0, pid, {get_cpuset_policy_profile_name((SchedPolicy)grp)}))
+    const int uid = uid_from_pid(pid);
+    if (uid < 0) {
+        signalExceptionForGroupError(env, ESRCH, pid);
+        return;
+    }
+    if (!SetProcessProfilesCached(uid, pid, {get_cpuset_policy_profile_name((SchedPolicy)grp)}))
         signalExceptionForGroupError(env, errno ? errno : EPERM, pid);
 }