[PATCH] kprobes: Rollback post_handler on failed arm_kprobe()

[Chuang W <nashuiliang@gmail.com>]

In a scenario where livepatch and aggrprobe coexist, if arm_kprobe()
returns an error, ap.post_handler, while has been modified to
p.post_handler, is not rolled back.

When ap.post_handler is not NULL (not rolled back), the caller (e.g.
register_kprobe/enable_kprobe) of arm_kprobe_ftrace() will always fail.

Fixes: 12310e343755 ("kprobes: Propagate error from arm_kprobe_ftrace()")
Signed-off-by: Chuang W <nashuiliang@gmail.com>
Cc: <stable@vger.kernel.org>
---
 kernel/kprobes.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index f214f8c088ed..0610b02a3a05 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1300,6 +1300,7 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 {
 	int ret = 0;
 	struct kprobe *ap = orig_p;
+	kprobe_post_handler_t old_post_handler = NULL;
 
 	cpus_read_lock();
 
@@ -1351,6 +1352,9 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 
 	/* Copy the insn slot of 'p' to 'ap'. */
 	copy_kprobe(ap, p);
+
+	/* save the old post_handler */
+	old_post_handler = ap->post_handler;
 	ret = add_new_kprobe(ap, p);
 
 out:
@@ -1365,6 +1369,7 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 			ret = arm_kprobe(ap);
 			if (ret) {
 				ap->flags |= KPROBE_FLAG_DISABLED;
+				ap->post_handler = old_post_handler;
 				list_del_rcu(&p->list);
 				synchronize_rcu();
 			}
-- 
2.34.1