commit c49b40380fb61729e7d5f6092f05183ccbe0d64e
author Suren Baghdasaryan <surenb@google.com> Thu Mar 21 17:10:09 2019 -0700
committer Suren Baghdasaryan <surenb@google.com> Mon Mar 25 16:22:10 2019 +0000
tree 61dc11a1e11da71e04542b7b8b749f91ea9ccfa0
parent 50c96add70fe9efe1c28c0fb923d631aafe34a29

libprocessgroup: make sure SetupCgroups is called once and only by init

SetupCgroups is called by init process during early-init stage and is not
supposed to be called again by anyone else. Ensure that the caller is the
init process, make sure cgroup.rc file is written only one time, keep the
file descriptor to cgroup.rc file open by the init process to ensure all
its further mappings stay valid even if the file is deleted.

Bug: 124774415
Test: build, run, verify no errors or warning in the logcat

Change-Id: I70ccec551fc07c380333566f618b969667dcf783
Signed-off-by: Suren Baghdasaryan <surenb@google.com>

libprocessgroup/cgroup_map.cpp

diff --git a/libprocessgroup/cgroup_map.cpp b/libprocessgroup/cgroup_map.cpp
index b3b497f..41a6e6e 100644
--- a/libprocessgroup/cgroup_map.cpp
+++ b/libprocessgroup/cgroup_map.cpp
@@ -229,9 +229,11 @@
 
 static bool WriteRcFile(const std::map<std::string, CgroupDescriptor>& descriptors) {
     std::string cgroup_rc_path = StringPrintf("%s/%s", CGROUPS_RC_DIR, CgroupMap::CGROUPS_RC_FILE);
-    unique_fd fd(TEMP_FAILURE_RETRY(open(cgroup_rc_path.c_str(),
-                                         O_CREAT | O_WRONLY | O_TRUNC | O_CLOEXEC,
-                                         S_IRUSR | S_IRGRP | S_IROTH)));
+    // Let init keep the FD open to prevent file mappings from becoming invalid
+    // in case the file gets deleted somehow
+    static unique_fd fd(TEMP_FAILURE_RETRY(open(cgroup_rc_path.c_str(),
+                                                O_CREAT | O_WRONLY | O_TRUNC | O_CLOEXEC,
+                                                S_IRUSR | S_IRGRP | S_IROTH)));
     if (fd < 0) {
         PLOG(ERROR) << "open() failed for " << cgroup_rc_path;
         return false;
@@ -412,6 +414,19 @@
 bool CgroupMap::SetupCgroups() {
     std::map<std::string, CgroupDescriptor> descriptors;
 
+    if (getpid() != 1) {
+        LOG(ERROR) << "Cgroup setup can be done only by init process";
+        return false;
+    }
+
+    // Make sure we do this only one time. No need for std::call_once because
+    // init is a single-threaded process
+    static bool setup_done = false;
+    if (setup_done) {
+        LOG(WARNING) << "Attempt to call SetupCgroups more than once";
+        return true;
+    }
+
     // load cgroups.json file
     if (!ReadDescriptors(&descriptors)) {
         LOG(ERROR) << "Failed to load cgroup description file";
@@ -449,6 +464,7 @@
         return false;
     }
 
+    setup_done = true;
     return true;
 }