From 2fd752ed77ab9880da927257b73294f29a199f1a Mon Sep 17 00:00:00 2001 From: Suren Baghdasaryan Date: Tue, 11 Jan 2022 15:23:09 -0800 Subject: psi: Fix uaf issue when psi trigger is destroyed while being polled commit a06247c6804f1a7c86a2e5398a4c1f1db1471848 upstream. With write operation on psi files replacing old trigger with a new one, the lifetime of its waitqueue is totally arbitrary. Overwriting an existing trigger causes its waitqueue to be freed and pending poll() will stumble on trigger->event_wait which was destroyed. Fix this by disallowing to redefine an existing psi trigger. If a write operation is used on a file descriptor with an already existing psi trigger, the operation will fail with EBUSY error. Also bypass a check for psi_disabled in the psi_trigger_destroy as the flag can be flipped after the trigger is created, leading to a memory leak. Fixes: 0e94682b73bf ("psi: introduce psi monitor") Reported-by: syzbot+cdb5dd11c97cc532efad@syzkaller.appspotmail.com Suggested-by: Linus Torvalds Analyzed-by: Eric Biggers Signed-off-by: Suren Baghdasaryan Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Eric Biggers Acked-by: Johannes Weiner Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20220111232309.1786347-1-surenb@google.com [surenb: backported to 5.4 kernel] CC: stable@vger.kernel.org # 5.4 Signed-off-by: Suren Baghdasaryan Signed-off-by: Greg Kroah-Hartman --- include/linux/psi.h | 2 +- include/linux/psi_types.h | 3 --- 2 files changed, 1 insertion(+), 4 deletions(-) (limited to 'include/linux') diff --git a/include/linux/psi.h b/include/linux/psi.h index 7b3de7321219..7712b5800927 100644 --- a/include/linux/psi.h +++ b/include/linux/psi.h @@ -31,7 +31,7 @@ void cgroup_move_task(struct task_struct *p, struct css_set *to); struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf, size_t nbytes, enum psi_res res); -void psi_trigger_replace(void **trigger_ptr, struct psi_trigger *t); +void psi_trigger_destroy(struct psi_trigger *t); __poll_t psi_trigger_poll(void **trigger_ptr, struct file *file, poll_table *wait); diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h index 07aaf9b82241..0023052eab23 100644 --- a/include/linux/psi_types.h +++ b/include/linux/psi_types.h @@ -120,9 +120,6 @@ struct psi_trigger { * events to one per window */ u64 last_event_time; - - /* Refcounting to prevent premature destruction */ - struct kref refcount; }; struct psi_group { -- cgit v1.2.3