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, 4 insertions, 2 deletions

diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index 6d1ed07bf312..2dc06ab35716 100644
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -27,6 +27,7 @@
  */
 void bacct_add_tsk(struct taskstats *stats, struct task_struct *tsk)
 {
+        const struct cred *tcred;
         struct timespec uptime, ts;
         u64 ac_etime;
 
@@ -53,10 +54,11 @@ void bacct_add_tsk(struct taskstats *stats, struct task_struct *tsk)
                 stats->ac_flag |= AXSIG;
         stats->ac_nice   = task_nice(tsk);
         stats->ac_sched  = tsk->policy;
-        stats->ac_uid    = tsk->cred->uid;
-        stats->ac_gid    = tsk->cred->gid;
         stats->ac_pid    = tsk->pid;
         rcu_read_lock();
+        tcred = __task_cred(tsk);
+        stats->ac_uid    = tcred->uid;
+        stats->ac_gid    = tcred->gid;
         stats->ac_ppid   = pid_alive(tsk) ?
                                 rcu_dereference(tsk->real_parent)->tgid : 0;
         rcu_read_unlock();