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>

10 files changed, 130 insertions, 81 deletions

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 2febf5165fa..ae8ef88ade3 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -447,7 +447,7 @@ static int audit_filter_rules(struct task_struct *tsk,
 			      struct audit_names *name,
 			      enum audit_state *state)
 {
-	struct cred *cred = tsk->cred;
+	const struct cred *cred = get_task_cred(tsk);
 	int i, j, need_sid = 1;
 	u32 sid;
 
@@ -642,8 +642,10 @@ static int audit_filter_rules(struct task_struct *tsk,
 			break;
 		}
 
-		if (!result)
+		if (!result) {
+			put_cred(cred);
 			return 0;
+		}
 	}
 	if (rule->filterkey && ctx)
 		ctx->filterkey = kstrdup(rule->filterkey, GFP_ATOMIC);
@@ -651,6 +653,7 @@ static int audit_filter_rules(struct task_struct *tsk,
 	case AUDIT_NEVER:    *state = AUDIT_DISABLED;	    break;
 	case AUDIT_ALWAYS:   *state = AUDIT_RECORD_CONTEXT; break;
 	}
+	put_cred(cred);
 	return 1;
 }
 
@@ -1229,7 +1232,7 @@ static void audit_log_fcaps(struct audit_buffer *ab, struct audit_names *name)
 
 static void audit_log_exit(struct audit_context *context, struct task_struct *tsk)
 {
-	struct cred *cred = tsk->cred;
+	const struct cred *cred;
 	int i, call_panic = 0;
 	struct audit_buffer *ab;
 	struct audit_aux_data *aux;
@@ -1239,13 +1242,14 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
 	context->pid = tsk->pid;
 	if (!context->ppid)
 		context->ppid = sys_getppid();
-	context->uid = cred->uid;
-	context->gid = cred->gid;
-	context->euid = cred->euid;
-	context->suid = cred->suid;
+	cred = current_cred();
+	context->uid   = cred->uid;
+	context->gid   = cred->gid;
+	context->euid  = cred->euid;
+	context->suid  = cred->suid;
 	context->fsuid = cred->fsuid;
-	context->egid = cred->egid;
-	context->sgid = cred->sgid;
+	context->egid  = cred->egid;
+	context->sgid  = cred->sgid;
 	context->fsgid = cred->fsgid;
 	context->personality = tsk->personality;
 
@@ -2088,7 +2092,7 @@ int audit_set_loginuid(struct task_struct *task, uid_t loginuid)
 			audit_log_format(ab, "login pid=%d uid=%u "
 				"old auid=%u new auid=%u"
 				" old ses=%u new ses=%u",
-				task->pid, task->cred->uid,
+				task->pid, task_uid(task),
 				task->loginuid, loginuid,
 				task->sessionid, sessionid);
 			audit_log_end(ab);
@@ -2471,7 +2475,7 @@ void __audit_ptrace(struct task_struct *t)
 
 	context->target_pid = t->pid;
 	context->target_auid = audit_get_loginuid(t);
-	context->target_uid = t->cred->uid;
+	context->target_uid = task_uid(t);
 	context->target_sessionid = audit_get_sessionid(t);
 	security_task_getsecid(t, &context->target_sid);
 	memcpy(context->target_comm, t->comm, TASK_COMM_LEN);
@@ -2490,6 +2494,7 @@ int __audit_signal_info(int sig, struct task_struct *t)
 	struct audit_aux_data_pids *axp;
 	struct task_struct *tsk = current;
 	struct audit_context *ctx = tsk->audit_context;
+	uid_t uid = current_uid(), t_uid = task_uid(t);
 
 	if (audit_pid && t->tgid == audit_pid) {
 		if (sig == SIGTERM || sig == SIGHUP || sig == SIGUSR1 || sig == SIGUSR2) {
@@ -2497,7 +2502,7 @@ int __audit_signal_info(int sig, struct task_struct *t)
 			if (tsk->loginuid != -1)
 				audit_sig_uid = tsk->loginuid;
 			else
-				audit_sig_uid = tsk->cred->uid;
+				audit_sig_uid = uid;
 			security_task_getsecid(tsk, &audit_sig_sid);
 		}
 		if (!audit_signals || audit_dummy_context())
@@ -2509,7 +2514,7 @@ int __audit_signal_info(int sig, struct task_struct *t)
 	if (!ctx->target_pid) {
 		ctx->target_pid = t->tgid;
 		ctx->target_auid = audit_get_loginuid(t);
-		ctx->target_uid = t->cred->uid;
+		ctx->target_uid = t_uid;
 		ctx->target_sessionid = audit_get_sessionid(t);
 		security_task_getsecid(t, &ctx->target_sid);
 		memcpy(ctx->target_comm, t->comm, TASK_COMM_LEN);
@@ -2530,7 +2535,7 @@ int __audit_signal_info(int sig, struct task_struct *t)
 
 	axp->target_pid[axp->pid_count] = t->tgid;
 	axp->target_auid[axp->pid_count] = audit_get_loginuid(t);
-	axp->target_uid[axp->pid_count] = t->cred->uid;
+	axp->target_uid[axp->pid_count] = t_uid;
 	axp->target_sessionid[axp->pid_count] = audit_get_sessionid(t);
 	security_task_getsecid(t, &axp->target_sid[axp->pid_count]);
 	memcpy(axp->target_comm[axp->pid_count], t->comm, TASK_COMM_LEN);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e210526e640..a512a75a556 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1279,7 +1279,7 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
 {
 	struct task_struct *tsk;
-	uid_t euid;
+	const struct cred *cred = current_cred(), *tcred;
 	int ret;
 
 	if (pid) {
@@ -1289,16 +1289,16 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
 			rcu_read_unlock();
 			return -ESRCH;
 		}
-		get_task_struct(tsk);
-		rcu_read_unlock();
 
-		euid = current_euid();
-		if (euid &&
-		    euid != tsk->cred->uid &&
-		    euid != tsk->cred->suid) {
-			put_task_struct(tsk);
+		tcred = __task_cred(tsk);
+		if (cred->euid &&
+		    cred->euid != tcred->uid &&
+		    cred->euid != tcred->suid) {
+			rcu_read_unlock();
 			return -EACCES;
 		}
+		get_task_struct(tsk);
+		rcu_read_unlock();
 	} else {
 		tsk = current;
 		get_task_struct(tsk);
diff --git a/kernel/exit.c b/kernel/exit.c
index e0f6e1892fb..bbc22530f2c 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -160,7 +160,10 @@ void release_task(struct task_struct * p)
 	int zap_leader;
 repeat:
 	tracehook_prepare_release_task(p);
-	atomic_dec(&p->cred->user->processes);
+	/* don't need to get the RCU readlock here - the process is dead and
+	 * can't be modifying its own credentials */
+	atomic_dec(&__task_cred(p)->user->processes);
+
 	proc_flush_task(p);
 	write_lock_irq(&tasklist_lock);
 	tracehook_finish_release_task(p);
@@ -1267,12 +1270,12 @@ static int wait_task_zombie(struct task_struct *p, int options,
 	unsigned long state;
 	int retval, status, traced;
 	pid_t pid = task_pid_vnr(p);
+	uid_t uid = __task_cred(p)->uid;
 
 	if (!likely(options & WEXITED))
 		return 0;
 
 	if (unlikely(options & WNOWAIT)) {
-		uid_t uid = p->cred->uid;
 		int exit_code = p->exit_code;
 		int why, status;
 
@@ -1393,7 +1396,7 @@ static int wait_task_zombie(struct task_struct *p, int options,
 	if (!retval && infop)
 		retval = put_user(pid, &infop->si_pid);
 	if (!retval && infop)
-		retval = put_user(p->cred->uid, &infop->si_uid);
+		retval = put_user(uid, &infop->si_uid);
 	if (!retval)
 		retval = pid;
 
@@ -1458,7 +1461,8 @@ static int wait_task_stopped(int ptrace, struct task_struct *p,
 	if (!unlikely(options & WNOWAIT))
 		p->exit_code = 0;
 
-	uid = p->cred->uid;
+	/* don't need the RCU readlock here as we're holding a spinlock */
+	uid = __task_cred(p)->uid;
 unlock_sig:
 	spin_unlock_irq(&p->sighand->siglock);
 	if (!exit_code)
@@ -1532,10 +1536,10 @@ static int wait_task_continued(struct task_struct *p, int options,
 	}
 	if (!unlikely(options & WNOWAIT))
 		p->signal->flags &= ~SIGNAL_STOP_CONTINUED;
+	uid = __task_cred(p)->uid;
 	spin_unlock_irq(&p->sighand->siglock);
 
 	pid = task_pid_vnr(p);
-	uid = p->cred->uid;
 	get_task_struct(p);
 	read_unlock(&tasklist_lock);
 
diff --git a/kernel/futex.c b/kernel/futex.c
index 28421d8210b..4fe790e89d0 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -439,15 +439,20 @@ static void free_pi_state(struct futex_pi_state *pi_state)
 static struct task_struct * futex_find_get_task(pid_t pid)
 {
 	struct task_struct *p;
-	uid_t euid = current_euid();
+	const struct cred *cred = current_cred(), *pcred;
 
 	rcu_read_lock();
 	p = find_task_by_vpid(pid);
-	if (!p || (euid != p->cred->euid &&
-		   euid != p->cred->uid))
+	if (!p) {
 		p = ERR_PTR(-ESRCH);
-	else
-		get_task_struct(p);
+	} else {
+		pcred = __task_cred(p);
+		if (cred->euid != pcred->euid &&
+		    cred->euid != pcred->uid)
+			p = ERR_PTR(-ESRCH);
+		else
+			get_task_struct(p);
+	}
 
 	rcu_read_unlock();
 
@@ -1831,7 +1836,7 @@ sys_get_robust_list(int pid, struct robust_list_head __user * __user *head_ptr,
 {
 	struct robust_list_head __user *head;
 	unsigned long ret;
-	uid_t euid = current_euid();
+	const struct cred *cred = current_cred(), *pcred;
 
 	if (!futex_cmpxchg_enabled)
 		return -ENOSYS;
@@ -1847,8 +1852,9 @@ sys_get_robust_list(int pid, struct robust_list_head __user * __user *head_ptr,
 		if (!p)
 			goto err_unlock;
 		ret = -EPERM;
-		if (euid != p->cred->euid &&
-		    euid != p->cred->uid &&
+		pcred = __task_cred(p);
+		if (cred->euid != pcred->euid &&
+		    cred->euid != pcred->uid &&
 		    !capable(CAP_SYS_PTRACE))
 			goto err_unlock;
 		head = p->robust_list;
diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c
index 2c3fd5ed34f..d607a5b9ee2 100644
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -135,7 +135,7 @@ compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr,
 {
 	struct compat_robust_list_head __user *head;
 	unsigned long ret;
-	uid_t euid = current_euid();
+	const struct cred *cred = current_cred(), *pcred;
 
 	if (!futex_cmpxchg_enabled)
 		return -ENOSYS;
@@ -151,8 +151,9 @@ compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr,
 		if (!p)
 			goto err_unlock;
 		ret = -EPERM;
-		if (euid != p->cred->euid &&
-		    euid != p->cred->uid &&
+		pcred = __task_cred(p);
+		if (cred->euid != pcred->euid &&
+		    cred->euid != pcred->uid &&
 		    !capable(CAP_SYS_PTRACE))
 			goto err_unlock;
 		head = p->compat_robust_list;
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 49849d12dd1..b9d5f4e4f6a 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -115,7 +115,7 @@ int ptrace_check_attach(struct task_struct *child, int kill)
 
 int __ptrace_may_access(struct task_struct *task, unsigned int mode)
 {
-	struct cred *cred = current->cred, *tcred = task->cred;
+	const struct cred *cred = current_cred(), *tcred;
 
 	/* May we inspect the given task?
 	 * This check is used both for attaching with ptrace
@@ -125,19 +125,23 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
 	 * because setting up the necessary parent/child relationship
 	 * or halting the specified task is impossible.
 	 */
-	uid_t uid = cred->uid;
-	gid_t gid = cred->gid;
 	int dumpable = 0;
 	/* Don't let security modules deny introspection */
 	if (task == current)
 		return 0;
-	if ((uid != tcred->euid ||
-	     uid != tcred->suid ||
-	     uid != tcred->uid  ||
-	     gid != tcred->egid ||
-	     gid != tcred->sgid ||
-	     gid != tcred->gid) && !capable(CAP_SYS_PTRACE))
+	rcu_read_lock();
+	tcred = __task_cred(task);
+	if ((cred->uid != tcred->euid ||
+	     cred->uid != tcred->suid ||
+	     cred->uid != tcred->uid  ||
+	     cred->gid != tcred->egid ||
+	     cred->gid != tcred->sgid ||
+	     cred->gid != tcred->gid) &&
+	    !capable(CAP_SYS_PTRACE)) {
+		rcu_read_unlock();
 		return -EPERM;
+	}
+	rcu_read_unlock();
 	smp_rmb();
 	if (task->mm)
 		dumpable = get_dumpable(task->mm);
diff --git a/kernel/sched.c b/kernel/sched.c
index 733c59e645a..92992e287b1 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -345,7 +345,9 @@ static inline struct task_group *task_group(struct task_struct *p)
 	struct task_group *tg;
 
 #ifdef CONFIG_USER_SCHED
-	tg = p->cred->user->tg;
+	rcu_read_lock();
+	tg = __task_cred(p)->user->tg;
+	rcu_read_unlock();
 #elif defined(CONFIG_CGROUP_SCHED)
 	tg = container_of(task_subsys_state(p, cpu_cgroup_subsys_id),
 				struct task_group, css);
@@ -5121,6 +5123,22 @@ __setscheduler(struct rq *rq, struct task_struct *p, int policy, int prio)
 	set_load_weight(p);
 }
 
+/*
+ * check the target process has a UID that matches the current process's
+ */
+static bool check_same_owner(struct task_struct *p)
+{
+	const struct cred *cred = current_cred(), *pcred;
+	bool match;
+
+	rcu_read_lock();
+	pcred = __task_cred(p);
+	match = (cred->euid == pcred->euid ||
+		 cred->euid == pcred->uid);
+	rcu_read_unlock();
+	return match;
+}
+
 static int __sched_setscheduler(struct task_struct *p, int policy,
 				struct sched_param *param, bool user)
 {
@@ -5128,7 +5146,6 @@ static int __sched_setscheduler(struct task_struct *p, int policy,
 	unsigned long flags;
 	const struct sched_class *prev_class = p->sched_class;
 	struct rq *rq;
-	uid_t euid;
 
 	/* may grab non-irq protected spin_locks */
 	BUG_ON(in_interrupt());
@@ -5181,9 +5198,7 @@ recheck:
 			return -EPERM;
 
 		/* can't change other user's priorities */
-		euid = current_euid();
-		if (euid != p->cred->euid &&
-		    euid != p->cred->uid)
+		if (!check_same_owner(p))
 			return -EPERM;
 	}
 
@@ -5394,7 +5409,6 @@ long sched_setaffinity(pid_t pid, const cpumask_t *in_mask)
 	cpumask_t cpus_allowed;
 	cpumask_t new_mask = *in_mask;
 	struct task_struct *p;
-	uid_t euid;
 	int retval;
 
 	get_online_cpus();
@@ -5415,11 +5429,8 @@ long sched_setaffinity(pid_t pid, const cpumask_t *in_mask)
 	get_task_struct(p);
 	read_unlock(&tasklist_lock);
 
-	euid = current_euid();
 	retval = -EPERM;
-	if (euid != p->cred->euid &&
-	    euid != p->cred->uid &&
-	    !capable(CAP_SYS_NICE))
+	if (!check_same_owner(p) && !capable(CAP_SYS_NICE))
 		goto out_unlock;
 
 	retval = security_task_setscheduler(p, 0, NULL);
diff --git a/kernel/signal.c b/kernel/signal.c
index 80e8a6489f9..84989124baf 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -177,6 +177,11 @@ int next_signal(struct sigpending *pending, sigset_t *mask)
 	return sig;
 }
 
+/*
+ * allocate a new signal queue record
+ * - this may be called without locks if and only if t == current, otherwise an
+ *   appopriate lock must be held to protect t's user_struct
+ */
 static struct sigqueue *__sigqueue_alloc(struct task_struct *t, gfp_t flags,
 					 int override_rlimit)
 {
@@ -184,11 +189,12 @@ static struct sigqueue *__sigqueue_alloc(struct task_struct *t, gfp_t flags,
 	struct user_struct *user;
 
 	/*
-	 * In order to avoid problems with "switch_user()", we want to make
-	 * sure that the compiler doesn't re-load "t->user"
+	 * We won't get problems with the target's UID changing under us
+	 * because changing it requires RCU be used, and if t != current, the
+	 * caller must be holding the RCU readlock (by way of a spinlock) and
+	 * we use RCU protection here
 	 */
-	user = t->cred->user;
-	barrier();
+	user = __task_cred(t)->user;
 	atomic_inc(&user->sigpending);
 	if (override_rlimit ||
 	    atomic_read(&user->sigpending) <=
@@ -562,12 +568,13 @@ static int rm_from_queue(unsigned long mask, struct sigpending *s)
 
 /*
  * Bad permissions for sending the signal
+ * - the caller must hold at least the RCU read lock
  */
 static int check_kill_permission(int sig, struct siginfo *info,
 				 struct task_struct *t)
 {
+	const struct cred *cred = current_cred(), *tcred;
 	struct pid *sid;
-	uid_t uid, euid;
 	int error;
 
 	if (!valid_signal(sig))
@@ -580,10 +587,11 @@ static int check_kill_permission(int sig, struct siginfo *info,
 	if (error)
 		return error;
 
-	uid = current_uid();
-	euid = current_euid();
-	if ((euid ^ t->cred->suid) && (euid ^ t->cred->uid) &&
-	    (uid  ^ t->cred->suid) && (uid  ^ t->cred->uid) &&
+	tcred = __task_cred(t);
+	if ((cred->euid ^ tcred->suid) &&
+	    (cred->euid ^ tcred->uid) &&
+	    (cred->uid  ^ tcred->suid) &&
+	    (cred->uid  ^ tcred->uid) &&
 	    !capable(CAP_KILL)) {
 		switch (sig) {
 		case SIGCONT:
@@ -1011,6 +1019,10 @@ struct sighand_struct *lock_task_sighand(struct task_struct *tsk, unsigned long
 	return sighand;
 }
 
+/*
+ * send signal info to all the members of a group
+ * - the caller must hold the RCU read lock at least
+ */
 int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
 {
 	unsigned long flags;
@@ -1032,8 +1044,8 @@ int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
 /*
  * __kill_pgrp_info() sends a signal to a process group: this is what the tty
  * control characters do (^C, ^Z etc)
+ * - the caller must hold at least a readlock on tasklist_lock
  */
-
 int __kill_pgrp_info(int sig, struct siginfo *info, struct pid *pgrp)
 {
 	struct task_struct *p = NULL;
@@ -1089,6 +1101,7 @@ int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
 {
 	int ret = -EINVAL;
 	struct task_struct *p;
+	const struct cred *pcred;
 
 	if (!valid_signal(sig))
 		return ret;
@@ -1099,9 +1112,11 @@ int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
 		ret = -ESRCH;
 		goto out_unlock;
 	}
-	if ((info == SEND_SIG_NOINFO || (!is_si_special(info) && SI_FROMUSER(info)))
-	    && (euid != p->cred->suid) && (euid != p->cred->uid)
-	    && (uid != p->cred->suid) && (uid != p->cred->uid)) {
+	pcred = __task_cred(p);
+	if ((info == SEND_SIG_NOINFO ||
+	     (!is_si_special(info) && SI_FROMUSER(info))) &&
+	    euid != pcred->suid && euid != pcred->uid &&
+	    uid  != pcred->suid && uid  != pcred->uid) {
 		ret = -EPERM;
 		goto out_unlock;
 	}
@@ -1372,10 +1387,9 @@ int do_notify_parent(struct task_struct *tsk, int sig)
 	 */
 	rcu_read_lock();
 	info.si_pid = task_pid_nr_ns(tsk, tsk->parent->nsproxy->pid_ns);
+	info.si_uid = __task_cred(tsk)->uid;
 	rcu_read_unlock();
 
-	info.si_uid = tsk->cred->uid;
-
 	thread_group_cputime(tsk, &cputime);
 	info.si_utime = cputime_to_jiffies(cputime.utime);
 	info.si_stime = cputime_to_jiffies(cputime.stime);
@@ -1443,10 +1457,9 @@ static void do_notify_parent_cldstop(struct task_struct *tsk, int why)
 	 */
 	rcu_read_lock();
 	info.si_pid = task_pid_nr_ns(tsk, tsk->parent->nsproxy->pid_ns);
+	info.si_uid = __task_cred(tsk)->uid;
 	rcu_read_unlock();
 
-	info.si_uid = tsk->cred->uid;
-
 	info.si_utime = cputime_to_clock_t(tsk->utime);
 	info.si_stime = cputime_to_clock_t(tsk->stime);
 
@@ -1713,7 +1726,7 @@ static int ptrace_signal(int signr, siginfo_t *info,
 		info->si_errno = 0;
 		info->si_code = SI_USER;
 		info->si_pid = task_pid_vnr(current->parent);
-		info->si_uid = current->parent->cred->uid;
+		info->si_uid = task_uid(current->parent);
 	}
 
 	/* If the (new) signal is now blocked, requeue it.  */
diff --git a/kernel/sys.c b/kernel/sys.c
index c4d6b59553e..ccc9eb736d3 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -112,14 +112,17 @@ EXPORT_SYMBOL(cad_pid);
 
 void (*pm_power_off_prepare)(void);
 
+/*
+ * set the priority of a task
+ * - the caller must hold the RCU read lock
+ */
 static int set_one_prio(struct task_struct *p, int niceval, int error)
 {
-	uid_t euid = current_euid();
+	const struct cred *cred = current_cred(), *pcred = __task_cred(p);
 	int no_nice;
 
-	if (p->cred->uid  != euid &&
-	    p->cred->euid != euid &&
-	    !capable(CAP_SYS_NICE)) {
+	if (pcred->uid  != cred->euid &&
+	    pcred->euid != cred->euid && !capable(CAP_SYS_NICE)) {
 		error = -EPERM;
 		goto out;
 	}
diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index 6d1ed07bf31..2dc06ab3571 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();