libprocessgroup: Remove unnecessary permissions change in uid/pid hierarchy

When a new process is launched it ensures that all files under its uid/
and uid/pid hierarchy are accessible by the user/group of that process.
If the directory already exists that means the access permissions have
been already set before, therefore we do not need to reset them again.
This also avoids a race between two processes in the same uid with one
process being launched and walking the uid/ directory while the other
process is being killed and changing the content of that directory. In
such a race the process walking uid/ might find the uid/pid directory of
the process being killed but by the time it tries to set its permissions
the directory might be removed because the process got killed. The
change eliminates the possibility of this race.

Bug: 192421915
Bug: 192512069
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I182298c36f6b0b4580ab59e440bd3aea16f5fbfe

1 files changed, 5 insertions, 1 deletions

diff --git a/libprocessgroup/processgroup.cpp b/libprocessgroup/processgroup.cpp
index 5c7a75dba..c824376e5 100644
--- a/libprocessgroup/processgroup.cpp
+++ b/libprocessgroup/processgroup.cpp
@@ -224,7 +224,11 @@ void removeAllProcessGroups() {
  * transferred for the user/group passed as uid/gid before system_server can properly access them.
  */
 static bool MkdirAndChown(const std::string& path, mode_t mode, uid_t uid, gid_t gid) {
-    if (mkdir(path.c_str(), mode) == -1 && errno != EEXIST) {
+    if (mkdir(path.c_str(), mode) == -1) {
+        if (errno == EEXIST) {
+            // Directory already exists and permissions have been set at the time it was created
+            return true;
+        }
         return false;
     }