Patch "fprobe: Ensure running fprobe_exit_handler() finished before calling rethook_free()" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    fprobe: Ensure running fprobe_exit_handler() finished before calling rethook_free()

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fprobe-ensure-running-fprobe_exit_handler-finished-before-calling-rethook_free.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 195b9cb5b288fec1c871ef89f78cc9a7461aad3a Mon Sep 17 00:00:00 2001
From: "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>
Date: Fri, 7 Jul 2023 23:03:19 +0900
Subject: fprobe: Ensure running fprobe_exit_handler() finished before calling rethook_free()

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

commit 195b9cb5b288fec1c871ef89f78cc9a7461aad3a upstream.

Ensure running fprobe_exit_handler() has finished before
calling rethook_free() in the unregister_fprobe() so that caller can free
the fprobe right after unregister_fprobe().

unregister_fprobe() ensured that all running fprobe_entry/exit_handler()
have finished by calling unregister_ftrace_function() which synchronizes
RCU. But commit 5f81018753df ("fprobe: Release rethook after the ftrace_ops
is unregistered") changed to call rethook_free() after
unregister_ftrace_function(). So call rethook_stop() to make rethook
disabled before unregister_ftrace_function() and ensure it again.

Here is the possible code flow that can call the exit handler after
unregister_fprobe().

------
 CPU1                              CPU2
 call unregister_fprobe(fp)
 ...
                                   __fprobe_handler()
                                   rethook_hook() on probed function
 unregister_ftrace_function()
                                   return from probed function
                                   rethook hooks
                                   find rh->handler == fprobe_exit_handler
                                   call fprobe_exit_handler()
 rethook_free():
   set rh->handler = NULL;
 return from unreigster_fprobe;
                                   call fp->exit_handler() <- (*)
------

(*) At this point, the exit handler is called after returning from
unregister_fprobe().

This fixes it as following;
------
 CPU1                              CPU2
 call unregister_fprobe()
 ...
 rethook_stop():
   set rh->handler = NULL;
                                   __fprobe_handler()
                                   rethook_hook() on probed function
 unregister_ftrace_function()
                                   return from probed function
                                   rethook hooks
                                   find rh->handler == NULL
                                   return from rethook
 rethook_free()
 return from unreigster_fprobe;
------

Link: https://lore.kernel.org/all/168873859949.156157.13039240432299335849.stgit@devnote2/

Fixes: 5f81018753df ("fprobe: Release rethook after the ftrace_ops is unregistered")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/rethook.h |    1 +
 kernel/trace/fprobe.c   |    3 +++
 kernel/trace/rethook.c  |   13 +++++++++++++
 3 files changed, 17 insertions(+)

--- a/include/linux/rethook.h
+++ b/include/linux/rethook.h
@@ -59,6 +59,7 @@ struct rethook_node {
 };
 
 struct rethook *rethook_alloc(void *data, rethook_handler_t handler);
+void rethook_stop(struct rethook *rh);
 void rethook_free(struct rethook *rh);
 void rethook_add_node(struct rethook *rh, struct rethook_node *node);
 struct rethook_node *rethook_try_get(struct rethook *rh);
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -307,6 +307,9 @@ int unregister_fprobe(struct fprobe *fp)
 		    fp->ops.saved_func != fprobe_kprobe_handler))
 		return -EINVAL;
 
+	if (fp->rethook)
+		rethook_stop(fp->rethook);
+
 	ret = unregister_ftrace_function(&fp->ops);
 	if (ret < 0)
 		return ret;
--- a/kernel/trace/rethook.c
+++ b/kernel/trace/rethook.c
@@ -54,6 +54,19 @@ static void rethook_free_rcu(struct rcu_
 }
 
 /**
+ * rethook_stop() - Stop using a rethook.
+ * @rh: the struct rethook to stop.
+ *
+ * Stop using a rethook to prepare for freeing it. If you want to wait for
+ * all running rethook handler before calling rethook_free(), you need to
+ * call this first and wait RCU, and call rethook_free().
+ */
+void rethook_stop(struct rethook *rh)
+{
+	WRITE_ONCE(rh->handler, NULL);
+}
+
+/**
  * rethook_free() - Free struct rethook.
  * @rh: the struct rethook to be freed.
  *


Patches currently in stable-queue which might be from mhiramat@xxxxxxxxxx are

queue-6.1/fprobe-release-rethook-after-the-ftrace_ops-is-unregistered.patch
queue-6.1/tracing-probes-fix-to-update-dynamic-data-counter-if-fetcharg-uses-it.patch
queue-6.1/fprobe-ensure-running-fprobe_exit_handler-finished-before-calling-rethook_free.patch
queue-6.1/tracing-fix-null-pointer-dereference-in-tracing_err_log_open.patch
queue-6.1/kernel-trace-fix-cleanup-logic-of-enable_trace_eprob.patch
queue-6.1/tracing-probes-fix-not-to-count-error-code-to-total-length.patch



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