CRED: Use RCU to access another task's creds and to release a task's own creds

Use RCU to access another task's creds and to release a task's own creds.
This means that it will be possible for the credentials of a task to be
replaced without another task (a) requiring a full lock to read them, and (b)
seeing deallocated memory.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 11 insertions, 5 deletions

diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
index 354c1ff17159..c5afc98e2675 100644
--- a/drivers/connector/cn_proc.c
+++ b/drivers/connector/cn_proc.c
@@ -106,6 +106,7 @@ void proc_id_connector(struct task_struct *task, int which_id)
         struct proc_event *ev;
         __u8 buffer[CN_PROC_MSG_SIZE];
         struct timespec ts;
+        const struct cred *cred;
 
         if (atomic_read(&proc_event_num_listeners) < 1)
                 return;
@@ -115,14 +116,19 @@ void proc_id_connector(struct task_struct *task, int which_id)
         ev->what = which_id;
         ev->event_data.id.process_pid = task->pid;
         ev->event_data.id.process_tgid = task->tgid;
+        rcu_read_lock();
+        cred = __task_cred(task);
         if (which_id == PROC_EVENT_UID) {
-                ev->event_data.id.r.ruid = task->cred->uid;
-                ev->event_data.id.e.euid = task->cred->euid;
+                ev->event_data.id.r.ruid = cred->uid;
+                ev->event_data.id.e.euid = cred->euid;
         } else if (which_id == PROC_EVENT_GID) {
-                ev->event_data.id.r.rgid = task->cred->gid;
-                ev->event_data.id.e.egid = task->cred->egid;
-        } else
+                ev->event_data.id.r.rgid = cred->gid;
+                ev->event_data.id.e.egid = cred->egid;
+        } else {
+                rcu_read_unlock();
                 return;
+        }
+        rcu_read_unlock();
         get_seq(&msg->seq, &ev->cpu);
         ktime_get_ts(&ts); /* get high res monotonic timestamp */
         put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);