[PATCH 1/3] kprobes: Fixed probe nodes not correctly removed when forcibly unoptimized

[Yang Jihong]

When unoptimize_kprobe forcibly unoptimize the kprobe, simply queue it in
the freeing_list, and do_free_cleaned_kprobes directly reclaims the kprobe
if unoptimizing_list is empty (see do_unoptimize_kprobes), which may cause
WARN or UAF problems.

The specific scenarios are as follows:

                          Thread1
arm_kprobe(p)
  mutex_lock(&kprobe_mutex)
  __arm_kprobe(kp)
    p = get_optimized_kprobe(p->addr)
    if (unlikely(_p))
      unoptimize_kprobe(_p, true)  // now _p is queued in freeing_list
  mutex_unlock(&kprobe_mutex)

                           Thread2
kprobe_optimizer
  mutex_lock(&kprobe_mutex)
  do_unoptimize_kprobes
    if (list_empty(&unoptimizing_list))
      return;  // here directly returned and does not process freeing_list.
  ...
  do_free_cleaned_kprobes
    foreach op in freeing_list:
      WARN_ON_ONCE(!kprobe_unused(&op->kp))  // WANR will be triggered here.
      free_aggr_kprobe((&op->kp)  // Delete op->kp directly, if access hash
                                  // list later, UAF problem will be triggered.
  mutex_unlock(&kprobe_mutex)

The freeing_list needs to be processed in do_unoptimize_kprobes regardless
of whether unoptimizing_list is empty.

Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
---
 kernel/kprobes.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 1c18ecf9f98b..0730e595f4c1 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -556,10 +556,9 @@ static void do_unoptimize_kprobes(void)
 	lockdep_assert_cpus_held();
 
 	/* Unoptimization must be done anytime */
-	if (list_empty(&unoptimizing_list))
-		return;
+	if (!list_empty(&unoptimizing_list))
+		arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list);
 
-	arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list);
 	/* Loop on 'freeing_list' for disarming */
 	list_for_each_entry_safe(op, tmp, &freeing_list, list) {
 		/* Switching from detour code to origin */
-- 
2.30.GIT