commit 812d7698d8728bba08c5abc27d58413d17f776de
author Bart Van Assche <bvanassche@google.com> Wed Mar 23 10:22:46 2022 -0700
committer Bart Van Assche <bvanassche@google.com> Fri Mar 25 07:32:56 2022 -0700
tree 84f3575a3068dc9a377e70f686ce813a7e4320d2
parent a6c82269e5e54c311098039cadf6a6ca0766010d

Fix the cgroup directory owner in createProcessGroupInternal()

Without this patch attempts to modify the blkio cgroup attributes by
/system/bin/mediaserver fail as follows:

03-23 09:27:59.542   517  1811 E libprocessgroup: Failed to write '100' to /sys/fs/cgroup/./uid_1013/pid_517/io.bfq.weight: Permission denied

This is because the mediaserver process is started as user 'media',
because the mediaserver process is not in the system group and hence
does not have permission to write into a directory with the following
owner, group and permissions:

vsoc_x86_64:/ # ls -ld /sys/fs/cgroup/./uid_1013/pid_517/io.bfq.weight
-rwxrwxr-x 1 system system 0 2022-03-23 09:27 /sys/fs/cgroup/./uid_1013/pid_517/io.bfq.weight

Bug: 213617178
Test: Booted Android in Cuttlefish and inspected logcat.
Change-Id: I788acc9a137ae29898177f492cae2f954a9c811c
Signed-off-by: Bart Van Assche <bvanassche@google.com>

libprocessgroup/processgroup.cpp

diff --git a/libprocessgroup/processgroup.cpp b/libprocessgroup/processgroup.cpp
index 54772b6..e910680 100644
--- a/libprocessgroup/processgroup.cpp
+++ b/libprocessgroup/processgroup.cpp
@@ -460,7 +460,6 @@
 
     struct stat cgroup_stat;
     mode_t cgroup_mode = 0750;
-    uid_t cgroup_uid = AID_SYSTEM;
     gid_t cgroup_gid = AID_SYSTEM;
     int ret = 0;
 
@@ -468,11 +467,10 @@
         PLOG(ERROR) << "Failed to get stats for " << cgroup;
     } else {
         cgroup_mode = cgroup_stat.st_mode;
-        cgroup_uid = cgroup_stat.st_uid;
         cgroup_gid = cgroup_stat.st_gid;
     }
 
-    if (!MkdirAndChown(uid_path, cgroup_mode, cgroup_uid, cgroup_gid)) {
+    if (!MkdirAndChown(uid_path, cgroup_mode, uid, cgroup_gid)) {
         PLOG(ERROR) << "Failed to make and chown " << uid_path;
         return -errno;
     }
@@ -486,7 +484,7 @@
 
     auto uid_pid_path = ConvertUidPidToPath(cgroup.c_str(), uid, initialPid);
 
-    if (!MkdirAndChown(uid_pid_path, cgroup_mode, cgroup_uid, cgroup_gid)) {
+    if (!MkdirAndChown(uid_pid_path, cgroup_mode, uid, cgroup_gid)) {
         PLOG(ERROR) << "Failed to make and chown " << uid_pid_path;
         return -errno;
     }