linux-kernel - Re: [PATCH v2 3/6] tracing: Use copy_from_user_nul() instead of copy_from

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Message-ID: <20260113130359.43f5411a@fedora>
Date: Tue, 13 Jan 2026 13:03:59 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Yury Norov <ynorov@...dia.com>
Cc: Fushuai Wang <fushuai.wang@...ux.dev>, tglx@...nel.org,
 peterz@...radead.org, mathieu.desnoyers@...icios.com,
 akpm@...ux-foundation.org, aliceryhl@...gle.com, yury.norov@...il.com,
 vmalik@...hat.com, kees@...nel.org, dave.hansen@...ux.intel.com,
 luto@...nel.org, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
 mhiramat@...nel.org, brauner@...nel.org, jack@...e.cz, cyphar@...har.com,
 linux-kernel@...r.kernel.org, x86@...nel.org,
 linux-trace-kernel@...r.kernel.org, wangfushuai@...du.com
Subject: Re: [PATCH v2 3/6] tracing: Use copy_from_user_nul() instead of
 copy_from_user()

On Tue, 13 Jan 2026 12:05:13 -0500
Yury Norov <ynorov@...dia.com> wrote:

> On Mon, Jan 12, 2026 at 03:30:36PM +0800, Fushuai Wang wrote:
> > From: Fushuai Wang <wangfushuai@...du.com>
> > 
> > Use copy_from_user_nul() instead of copy_from_user() to simplify
> > the code.
> > 
> > No functional change.
> > 
> > Signed-off-by: Fushuai Wang <wangfushuai@...du.com>
> > ---
> >  kernel/trace/trace.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index baec63134ab6..b6ffd006fcf9 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -11266,10 +11266,9 @@ ssize_t trace_parse_run_command(struct file *file, const char __user *buffer,
> >  		if (size >= WRITE_BUFSIZE)
> >  			size = WRITE_BUFSIZE - 1;
> >  
> > -		if (copy_from_user(kbuf, buffer + done, size))
> > +		if (copy_from_user_nul(kbuf, buffer + done, size))
> >  			return -EFAULT;  
> 
> This hides the original error. Can you switch it to:
> 
>                 err = copy_xxx();
>                 if (err)
>                         return err;

No, the current way is fine. It's failing on reading user space. EFAULT
is good enough.

-- Steve


> 
> I understand that in this case EFAULT is the only possible error, but
> the above pattern is really error-prone, and is reproduced again and
> again over the kernel.
> 
> > -		kbuf[size] = '\0';
> >  		buf = kbuf;
> >  		do {
> >  			tmp = strchr(buf, '\n');
> > -- 
> > 2.36.1