Unverified Commit 0c9bd6bc authored by Tycho Andersen's avatar Tycho Andersen Committed by Christian Brauner
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pidfd: getfd should always report ESRCH if a task is exiting 



We can get EBADF from pidfd_getfd() if a task is currently exiting,
which might be confusing. Let's check PF_EXITING, and just report ESRCH
if so.

I chose PF_EXITING, because it is set in exit_signals(), which is called
before exit_files(). Since ->exit_status is mostly set after
exit_files() in exit_notify(), using that still leaves a window open for
the race.

Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarTycho Andersen <tandersen@netflix.com>
Link: https://lore.kernel.org/r/20240206192357.81942-1-tycho@tycho.pizza


Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 83b290c9

kernel/pid.c

+20 −1
Original line number Diff line number Diff line
@@ -678,7 +678,26 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd) 


	up_read(&task->signal->exec_update_lock);



	return file ?: ERR_PTR(-EBADF);

	if (!file) {

		/*

		 * It is possible that the target thread is exiting; it can be

		 * either:

		 * 1. before exit_signals(), which gives a real fd

		 * 2. before exit_files() takes the task_lock() gives a real fd

		 * 3. after exit_files() releases task_lock(), ->files is NULL;

		 *    this has PF_EXITING, since it was set in exit_signals(),

		 *    __pidfd_fget() returns EBADF.

		 * In case 3 we get EBADF, but that really means ESRCH, since

		 * the task is currently exiting and has freed its files

		 * struct, so we fix it up.

		 */

		if (task->flags & PF_EXITING)

			file = ERR_PTR(-ESRCH);

		else

			file = ERR_PTR(-EBADF);

	}



	return file;

}



static int pidfd_getfd(struct pid *pid, int fd)