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Commit 6ae40e3f authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

posix-cpu-timers: Provide task validation functions 



The code contains three slightly different copies of validating whether a
given clock resolves to a valid task and whether the current caller has
permissions to access it.

Create central functions. Replace check_clock() as a first step and rename
it to something sensible.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190821192919.326097175@linutronix.de
parent a42e43c3

kernel/time/posix-cpu-timers.c

+44 −21
Original line number Diff line number Diff line
@@ -35,27 +35,52 @@ void update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new) 
	spin_unlock_irq(&task->sighand->siglock);

}



static int check_clock(const clockid_t which_clock)

/*

 * Functions for validating access to tasks.

 */

static struct task_struct *lookup_task(const pid_t pid, bool thread)

{

	int error = 0;

	struct task_struct *p;

	const pid_t pid = CPUCLOCK_PID(which_clock);



	if (CPUCLOCK_WHICH(which_clock) >= CPUCLOCK_MAX)

		return -EINVAL;

	if (!pid)

		return thread ? current : current->group_leader;



	if (pid == 0)

		return 0;



	rcu_read_lock();

	p = find_task_by_vpid(pid);

	if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ?

		   same_thread_group(p, current) : has_group_leader_pid(p))) {

		error = -EINVAL;

	if (!p || p == current)

		return p;

	if (thread)

		return same_thread_group(p, current) ? p : NULL;

	if (p == current)

		return p;

	return has_group_leader_pid(p) ? p : NULL;

}



static struct task_struct *__get_task_for_clock(const clockid_t clock,

						bool getref)

{

	const bool thread = !!CPUCLOCK_PERTHREAD(clock);

	const pid_t pid = CPUCLOCK_PID(clock);

	struct task_struct *p;



	if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)

		return NULL;



	rcu_read_lock();

	p = lookup_task(pid, thread);

	if (p && getref)

		get_task_struct(p);

	rcu_read_unlock();

	return p;

}



	return error;

static inline struct task_struct *get_task_for_clock(const clockid_t clock)

{

	return __get_task_for_clock(clock, true);

}



static inline int validate_clock_permissions(const clockid_t clock)

{

	return __get_task_for_clock(clock, false) ? 0 : -EINVAL;

}



/*
@@ -125,7 +150,8 @@ static inline u64 virt_ticks(struct task_struct *p) 
static int

posix_cpu_clock_getres(const clockid_t which_clock, struct timespec64 *tp)

{

	int error = check_clock(which_clock);

	int error = validate_clock_permissions(which_clock);



	if (!error) {

		tp->tv_sec = 0;

		tp->tv_nsec = ((NSEC_PER_SEC + HZ - 1) / HZ);
@@ -142,19 +168,16 @@ posix_cpu_clock_getres(const clockid_t which_clock, struct timespec64 *tp) 
}



static int

posix_cpu_clock_set(const clockid_t which_clock, const struct timespec64 *tp)

posix_cpu_clock_set(const clockid_t clock, const struct timespec64 *tp)

{

	int error = validate_clock_permissions(clock);



	/*

	 * You can never reset a CPU clock, but we check for other errors

	 * in the call before failing with EPERM.

	 */

	int error = check_clock(which_clock);

	if (error == 0) {

		error = -EPERM;

	return error ? : -EPERM;

}

	return error;

}





/*

 * Sample a per-thread clock for the given task.