linux-kernel - Re: [PATCH] traing: Fix memory leak of iter->temp when reading trace

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Date:   Thu, 13 Jul 2023 10:47:54 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Zheng Yejian <zhengyejian1@...wei.com>
Cc:     <mhiramat@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH] traing: Fix memory leak of iter->temp when reading
 trace_pipe

On Thu, 13 Jul 2023 22:23:20 +0800
Zheng Yejian <zhengyejian1@...wei.com> wrote:

> On 2023/7/13 22:14, Zheng Yejian wrote:
> > kmemleak reports:
> >    unreferenced object 0xffff88814d14e200 (size 256):
> >      comm "cat", pid 336, jiffies 4294871818 (age 779.490s)
> >      hex dump (first 32 bytes):
> >        04 00 01 03 00 00 00 00 08 00 00 00 00 00 00 00  ................
> >        0c d8 c8 9b ff ff ff ff 04 5a ca 9b ff ff ff ff  .........Z......
> >      backtrace:
> >        [<ffffffff9bdff18f>] __kmalloc+0x4f/0x140
> >        [<ffffffff9bc9238b>] trace_find_next_entry+0xbb/0x1d0
> >        [<ffffffff9bc9caef>] trace_print_lat_context+0xaf/0x4e0
> >        [<ffffffff9bc94490>] print_trace_line+0x3e0/0x950
> >        [<ffffffff9bc95499>] tracing_read_pipe+0x2d9/0x5a0
> >        [<ffffffff9bf03a43>] vfs_read+0x143/0x520
> >        [<ffffffff9bf04c2d>] ksys_read+0xbd/0x160
> >        [<ffffffff9d0f0edf>] do_syscall_64+0x3f/0x90
> >        [<ffffffff9d2000aa>] entry_SYSCALL_64_after_hwframe+0x6e/0xd8
> > 
> > when reading file 'trace_pipe', 'iter->temp' is allocated or relocated
> > in trace_find_next_entry() but not freed before 'trace_pipe' is closed.
> > 
> > To fix it, free 'iter->temp' in tracing_release_pipe().
> >   
> 
> Sorry, forget the Fixes tag:(
> 
> Is following Fixes right?
> Fixes: ff895103a84a ("tracing: Save off entry when peeking at next entry")

That's the one I already added ;-)

Don't worry too much about adding fixes, I will always analyze a fix patch
to find out what it actually fixes. If you add one, I'll still confirm it.

-- Steve

> 
> > Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
> > ---
> >   kernel/trace/trace.c | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index 4529e264cb86..94cfaa884578 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -6764,6 +6764,7 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)
> >   
> >   	free_cpumask_var(iter->started);
> >   	kfree(iter->fmt);
> > +	kfree(iter->temp);
> >   	mutex_destroy(&iter->mutex);
> >   	kfree(iter);
> >