It's currently possible to create pidfds for kthreads but it is unclear what that is supposed to mean. Until we have use-cases for it and we figured out what behavior we want block the creation of pidfds for kthreads. Link: https://lore.kernel.org/r/20240731-gleis-mehreinnahmen-6bbadd128383@brauner Fixes: 32fcb426ec00 ("pid: add pidfd_open()") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx> diff --git a/kernel/fork.c b/kernel/fork.c index cc760491f201..18bdc87209d0 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2053,11 +2053,24 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re */ int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret) { - bool thread = flags & PIDFD_THREAD; - - if (!pid || !pid_has_task(pid, thread ? PIDTYPE_PID : PIDTYPE_TGID)) + if (!pid) return -EINVAL; + scoped_guard(rcu) { + struct task_struct *tsk; + + if (flags & PIDFD_THREAD) + tsk = pid_task(pid, PIDTYPE_PID); + else + tsk = pid_task(pid, PIDTYPE_TGID); + if (!tsk) + return -EINVAL; + + /* Don't create pidfds for kernel threads for now. */ + if (tsk->flags & PF_KTHREAD) + return -EINVAL; + } + return __pidfd_prepare(pid, flags, ret); } @@ -2403,6 +2416,12 @@ __latent_entropy struct task_struct *copy_process( if (clone_flags & CLONE_PIDFD) { int flags = (clone_flags & CLONE_THREAD) ? PIDFD_THREAD : 0; + /* Don't create pidfds for kernel threads for now. */ + if (args->kthread) { + retval = -EINVAL; + goto bad_fork_free_pid; + } + /* Note that no task has been attached to @pid yet. */ retval = __pidfd_prepare(pid, flags, &pidfile); if (retval < 0)
