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.
Fixes: 32fcb426ec00 ("pid: add pidfd_open()")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
kernel/fork.c | 25 ++++++++++++++++++++++---
1 file changed, 22 insertions(+), 3 deletions(-)
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)
--
2.43.0
