linux-kernel - Re: [PATCH v2] perf/core: use strndup_user() instead of buggy open-coded version

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Date:   Thu, 21 Feb 2019 09:20:57 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, Song Liu <songliubraving@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v2] perf/core: use strndup_user() instead of buggy
 open-coded version

Hi Jann,

On Wed, 20 Feb 2019 17:54:43 +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, for stable, this is good. For the long term, I think we should
fix strndup_user() to return -E2BUG when the user string is longer
than max.

Thank you,

> Fixes: 0eadcc7a7bc0 ("perf/core: Fix perf_uprobe_init()")
> Signed-off-by: Jann Horn <jannh@...gle.com>
> ---
> v2:
>  - be compatible with existing error codes (Masami Hiramatsu)
> 
>  kernel/trace/trace_event_perf.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> index 76217bbef815..4629a6104474 100644
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -299,15 +299,13 @@ 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)) {
> +		ret = PTR_ERR(path);
> +		return (ret == -EINVAL) ? -E2BIG : ret;
> +	}
>  	if (path[0] == '\0') {
>  		ret = -EINVAL;
>  		goto out;
> -- 
> 2.21.0.rc0.258.g878e2cd30e-goog
> 


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