linux-kernel - Re: [PATCH] perf/core: use strndup_user() instead of buggy open-coded version

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Message-Id: <20190219235122.b9f8c6c47392a27131526018@kernel.org>
Date:   Tue, 19 Feb 2019 23:51:22 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Jann Horn <jannh@...gle.com>, Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, Song Liu <songliubraving@...com>
Subject: Re: [PATCH] perf/core: use strndup_user() instead of buggy
 open-coded version

On Tue, 19 Feb 2019 20:45:02 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Mon, 18 Feb 2019 23:07:23 +0100
> Jann Horn <jannh@...gle.com> wrote:
> 
> > The first version of this method was missing the check for
> > `ret == PATH_MAX`; then such a check was added, but it didn't call kfree()
> > on error, so there was still a small memory leak in the error case.
> > Fix it by using strndup_user() instead of open-coding it.
> > 
> 
> This looks good to me.
> 
> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>

BTW, I think it should note that if the string is longer than PATH_MAX.
caller will receive -EINVAL instead of -E2BIG with this fix.

Thank you,

> 
> Thank you!
> 
> > Fixes: 0eadcc7a7bc0 ("perf/core: Fix perf_uprobe_init()")
> > Signed-off-by: Jann Horn <jannh@...gle.com>
> > ---
> > compile-tested only
> > 
> >  kernel/trace/trace_event_perf.c | 14 +++++---------
> >  1 file changed, 5 insertions(+), 9 deletions(-)
> > 
> > diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> > index 76217bbef815..c744b02081c3 100644
> > --- a/kernel/trace/trace_event_perf.c
> > +++ b/kernel/trace/trace_event_perf.c
> > @@ -299,15 +299,11 @@ int perf_uprobe_init(struct perf_event *p_event,
> >  
> >  	if (!p_event->attr.uprobe_path)
> >  		return -EINVAL;
> > -	path = kzalloc(PATH_MAX, GFP_KERNEL);
> > -	if (!path)
> > -		return -ENOMEM;
> > -	ret = strncpy_from_user(
> > -		path, u64_to_user_ptr(p_event->attr.uprobe_path), PATH_MAX);
> > -	if (ret == PATH_MAX)
> > -		return -E2BIG;
> > -	if (ret < 0)
> > -		goto out;
> > +
> > +	path = strndup_user(u64_to_user_ptr(p_event->attr.uprobe_path),
> > +			    PATH_MAX);
> > +	if (IS_ERR(path))
> > +		return PTR_ERR(path);
> >  	if (path[0] == '\0') {
> >  		ret = -EINVAL;
> >  		goto out;
> > -- 
> > 2.21.0.rc0.258.g878e2cd30e-goog
> > 
> 
> 
> -- 
> Masami Hiramatsu <mhiramat@...nel.org>


-- 
Masami Hiramatsu <mhiramat@...nel.org>