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Message-ID: <20240725131021.788374d0@gandalf.local.home>
Date: Thu, 25 Jul 2024 13:10:21 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Ajay Kaher <ajay.kaher@...adcom.com>
Cc: Mathias Krause <minipli@...ecurity.net>, Masami Hiramatsu
<mhiramat@...nel.org>, Ilkka Naulapää
<digirigawa@...il.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Al
Viro <viro@...iv.linux.org.uk>, linux-trace-kernel@...r.kernel.org,
linux-kernel@...r.kernel.org, regressions@...mhuis.info, Dan Carpenter
<dan.carpenter@...aro.org>, Vasavi Sirnapalli
<vasavi.sirnapalli@...adcom.com>, Alexey Makhalov
<alexey.makhalov@...adcom.com>, Florian Fainelli
<florian.fainelli@...adcom.com>
Subject: Re: tracing: user events UAF crash report
On Thu, 25 Jul 2024 22:00:14 +0530
Ajay Kaher <ajay.kaher@...adcom.com> wrote:
> Thread A (read event) Thread B (remove event)
>
> . worker_thread()
> . delayed_destroy_user_event()
> . -> acquire event_mutex
> . destroy_user_event()
> vfs_read() .
> seq_read() .
> f_start() -> acquire event_mutex eventfs_remove_dir()
> . (waiting) kfree(user)
> . (waiting) -> released event_mutex
> acquired event_mutex
> f_next()
> trace_get_fields():
Hmm, I wonder if this would fix it?
-- Steve
diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 3a2b46847c8b..e9ed2826ff46 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -321,6 +321,8 @@ static void user_event_put(struct user_event *user, bool locked)
*/
refcount_set(&user->refcnt, 1);
+ user->call.data = NULL;
+
if (WARN_ON_ONCE(!schedule_work(&user->put_work))) {
/*
* If we fail we must wait for an admin to attempt delete or
@@ -973,6 +975,11 @@ size_t copy_nofault(void *addr, size_t bytes, struct iov_iter *i)
static struct list_head *user_event_get_fields(struct trace_event_call *call)
{
struct user_event *user = (struct user_event *)call->data;
+ static LIST_HEAD(head);
+
+ /* If the user event is about to be deleted, return no fields */
+ if (!user)
+ return &head;
return &user->fields;
}
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