[PATCH] kprobes: Update ftrace_ops when clearing ftrace-based aggrprobe's post_handler

[Li Huafei]

In __unregister_kprobe_top(), if the currently unregistered probe has
post_handler but other child probes of the aggrprobe do not have
post_handler, the post_handler of the aggrprobe is cleared. If this is
a ftrace-based probe, there is a problem. In later calls to
disarm_kprobe(), we will use kprobe_ftrace_ops because post_handler is
NULL. But we're armed with kprobe_ipmodify_ops. This triggers a WARN in
__disarm_kprobe_ftrace() and may even cause use-after-free:

  Failed to disarm kprobe-ftrace at kernel_clone+0x0/0x3c0 (error -2)
  WARNING: CPU: 5 PID: 137 at kernel/kprobes.c:1135 __disarm_kprobe_ftrace.isra.21+0xcf/0xe0
  Modules linked in: testKprobe_007(-)
  CPU: 5 PID: 137 Comm: rmmod Not tainted 6.1.0-rc4-dirty #18
  [...]
  Call Trace:
   <TASK>
   __disable_kprobe+0xcd/0xe0
   __unregister_kprobe_top+0x12/0x150
   ? mutex_lock+0xe/0x30
   unregister_kprobes.part.23+0x31/0xa0
   unregister_kprobe+0x32/0x40
   __x64_sys_delete_module+0x15e/0x260
   ? do_user_addr_fault+0x2cd/0x6b0
   do_syscall_64+0x3a/0x90
   entry_SYSCALL_64_after_hwframe+0x63/0xcd
   [...]

For ftrace kprobe, update post_handler at the same time update
ftrace_ops, moving it from kprobe_ipmodify_ops to kprobe_ftrace_ops.

Fixes: 0bc11ed5ab60 ("kprobes: Allow kprobes coexist with livepatch")
Reported-by: Zhao Gongyi <zhaogongyi@xxxxxxxxxx>
Signed-off-by: Li Huafei <lihuafei1@xxxxxxxxxx>
---
 kernel/kprobes.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index cd9f5a66a690..f8bec48a9cf9 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1766,7 +1766,17 @@ static int __unregister_kprobe_top(struct kprobe *p)
 				if ((list_p != p) && (list_p->post_handler))
 					goto noclean;
 			}
-			ap->post_handler = NULL;
+			/*
+			 * For ftrace kprobe, we need to update ftrace_ops
+			 * at the same time as we update post_handler, moving
+			 * it from kprobe_ipmodify_ops to kprobe_ftrace_ops.
+			 */
+			if (unlikely(kprobe_ftrace(ap))) {
+				disarm_kprobe(ap, false);
+				ap->post_handler = NULL;
+				arm_kprobe(ap);
+			} else
+				ap->post_handler = NULL;
 		}
 noclean:
 		/*
-- 
2.17.1