From: Christian Brauner <brauner@xxxxxxxxxx> commit 3b5bbe798b2451820e74243b738268f51901e7d0 upstream. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/fork.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-) --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2069,11 +2069,24 @@ static int __pidfd_prepare(struct pid *p */ 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); } @@ -2419,6 +2432,12 @@ __latent_entropy struct task_struct *cop 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) Patches currently in stable-queue which might be from brauner@xxxxxxxxxx are queue-6.10/vfs-don-t-evict-inode-under-the-inode-lru-traversing-context.patch queue-6.10/netfs-ceph-revert-netfs-remove-deprecated-use-of-pg_private_2-as-a-second-writeback-flag.patch queue-6.10/fs-netfs-fscache_cookie-add-missing-n_accesses-check.patch queue-6.10/pidfd-prevent-creation-of-pidfds-for-kthreads.patch
