* [PATCH v2] fprobe: Ensure running fprobe_exit_handler() finished before calling rethook_free()
@ 2023-07-07 14:03 Masami Hiramatsu (Google)
2023-07-10 22:04 ` Steven Rostedt
0 siblings, 1 reply; 3+ messages in thread
From: Masami Hiramatsu (Google) @ 2023-07-07 14:03 UTC (permalink / raw)
To: Jiri Olsa, Steven Rostedt
Cc: Masami Hiramatsu, Mark Rutland, lkml, linux-trace-kernel, bpf
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
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;
------
Fixes: 5f81018753df ("fprobe: Release rethook after the ftrace_ops is unregistered")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v2:
- Update changelog to add a problematic code flow.
---
include/linux/rethook.h | 1 +
kernel/trace/fprobe.c | 3 +++
kernel/trace/rethook.c | 13 +++++++++++++
3 files changed, 17 insertions(+)
diff --git a/include/linux/rethook.h b/include/linux/rethook.h
index c8ac1e5afcd1..bdbe6717f45a 100644
--- 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);
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 0121e8c0d54e..75517667b54f 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -364,6 +364,9 @@ 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;
diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
index 60f6cb2b486b..468006cce7ca 100644
--- a/kernel/trace/rethook.c
+++ b/kernel/trace/rethook.c
@@ -53,6 +53,19 @@ static void rethook_free_rcu(struct rcu_head *head)
kfree(rh);
}
+/**
+ * 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.
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] fprobe: Ensure running fprobe_exit_handler() finished before calling rethook_free()
2023-07-07 14:03 [PATCH v2] fprobe: Ensure running fprobe_exit_handler() finished before calling rethook_free() Masami Hiramatsu (Google)
@ 2023-07-10 22:04 ` Steven Rostedt
2023-07-11 0:06 ` Masami Hiramatsu
0 siblings, 1 reply; 3+ messages in thread
From: Steven Rostedt @ 2023-07-10 22:04 UTC (permalink / raw)
To: Masami Hiramatsu (Google)
Cc: Jiri Olsa, Mark Rutland, lkml, linux-trace-kernel, bpf
On Fri, 7 Jul 2023 23:03:19 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
> 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;
> ------
>
>
> Fixes: 5f81018753df ("fprobe: Release rethook after the ftrace_ops is unregistered")
> Cc: stable@vger.kernel.org
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Looks good.
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
> Changes in v2:
> - Update changelog to add a problematic code flow.
Nit, for making forensic analysis easier in the future, I now always add a
link to the previous version. That is:
Changes since v1: https://lore.kernel.org/linux-trace-kernel/168796344232.46347.7947681068822514750.stgit@devnote2/
- Update changelog to add a problematic code flow.
-- Steve
> ---
> include/linux/rethook.h | 1 +
> kernel/trace/fprobe.c | 3 +++
> kernel/trace/rethook.c | 13 +++++++++++++
> 3 files changed, 17 insertions(+)
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] fprobe: Ensure running fprobe_exit_handler() finished before calling rethook_free()
2023-07-10 22:04 ` Steven Rostedt
@ 2023-07-11 0:06 ` Masami Hiramatsu
0 siblings, 0 replies; 3+ messages in thread
From: Masami Hiramatsu @ 2023-07-11 0:06 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Jiri Olsa, Mark Rutland, lkml, linux-trace-kernel, bpf
On Mon, 10 Jul 2023 18:04:22 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 7 Jul 2023 23:03:19 +0900
> "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
>
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> >
> > 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;
> > ------
> >
> >
> > Fixes: 5f81018753df ("fprobe: Release rethook after the ftrace_ops is unregistered")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
> Looks good.
>
> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Thank you :)
>
>
> > ---
> > Changes in v2:
> > - Update changelog to add a problematic code flow.
>
> Nit, for making forensic analysis easier in the future, I now always add a
> link to the previous version. That is:
>
> Changes since v1: https://lore.kernel.org/linux-trace-kernel/168796344232.46347.7947681068822514750.stgit@devnote2/
> - Update changelog to add a problematic code flow.
OK, I'll add it for an isolated patch too.
Thanks!
>
> -- Steve
>
>
> > ---
> > include/linux/rethook.h | 1 +
> > kernel/trace/fprobe.c | 3 +++
> > kernel/trace/rethook.c | 13 +++++++++++++
> > 3 files changed, 17 insertions(+)
> >
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-07-07 14:03 [PATCH v2] fprobe: Ensure running fprobe_exit_handler() finished before calling rethook_free() Masami Hiramatsu (Google)
2023-07-10 22:04 ` Steven Rostedt
2023-07-11 0:06 ` Masami Hiramatsu
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