linux-kernel - Re: [PATCH] tracing/timerlat: Check tlat_var for NULL in timerlat_fd

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240822103443.6a6ae051@gandalf.local.home>
Date: Thu, 22 Aug 2024 10:34:43 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>
Cc: tglozar@...hat.com, linux-trace-kernel@...r.kernel.org,
 linux-kernel@...r.kernel.org, jkacur@...hat.com
Subject: Re: [PATCH] tracing/timerlat: Check tlat_var for NULL in
 timerlat_fd_release

On Thu, 22 Aug 2024 08:20:52 -0300
"Luis Claudio R. Goncalves" <lgoncalv@...hat.com> wrote:

> You mean the 
> 
> +	if (!tlat_var->kthread) {
> +		/* the fd has been closed already */
> 
> bit or the kthread handling in rtla itself?
> 
> As Tomas already said, thank you for testing and reviewing the suggested fix!

The close only happens once, but the kthread does get freed elsewhere.

I used my new persistent ring buffer to debug this! I'll be posting some
more patches that allow trace_printk() and friends to use the persistent
ring buffer (or any instance) soon.

For this bug, I would recommend instead doing:

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 66a871553d4a..53de719f35cb 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -2579,7 +2587,8 @@ static int timerlat_fd_release(struct inode *inode, struct file *file)
 	osn_var = per_cpu_ptr(&per_cpu_osnoise_var, cpu);
 	tlat_var = per_cpu_ptr(&per_cpu_timerlat_var, cpu);

-	hrtimer_cancel(&tlat_var->timer);
+	if (tlat_var->kthread)
+		hrtimer_cancel(&tlat_var->timer);
 	memset(tlat_var, 0, sizeof(*tlat_var));

 	osn_var->sampling = 0;

-- Steve