linux-kernel - Re: [PATCH] ftrace: Replaces simple

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Message-Id: <20231120135742.0abfc6bb7ccdd985990c68a4@kernel.org>
Date:   Mon, 20 Nov 2023 13:57:42 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Yuran Pereira <yuran.pereira@...mail.com>
Cc:     linux-trace-kernel@...r.kernel.org, mark.rutland@....com,
        rostedt@...dmis.org, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] ftrace: Replaces simple_strtoul in ftrace

On Mon, 20 Nov 2023 05:46:13 +0530
Yuran Pereira <yuran.pereira@...mail.com> wrote:

> The function simple_strtoul performs no error checking in scenarios
> where the input value overflows the intended output variable.
> This results in this function successfully returning, even when the
> output does not match the input string (aka the function returns
> successfully even when the result is wrong).
> 
> Or as it was mentioned [1], "...simple_strtol(), simple_strtoll(),
> simple_strtoul(), and simple_strtoull() functions explicitly ignore
> overflows, which may lead to unexpected results in callers."
> Hence, the use of those functions is discouraged.
> 
> This patch replaces all uses of the simple_strtoul with the safer
> alternatives kstrtoul and kstruint.
> 
> Callers affected:
> - add_rec_by_index
> - set_graph_max_depth_function
> 
> Side effects of this patch:
> - Since `fgraph_max_depth` is an `unsigned int`, this patch uses
>   kstrtouint instead of kstrtoul to avoid any compiler warnings
>   that could originate from calling the latter.
> - This patch ensures that the callers of kstrtou* return accordingly
>   when kstrtoul and kstruint fail for some reason.
>   In this case, both callers this patch is addressing return 0 on error.
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull
> 

This looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thank you!

> Signed-off-by: Yuran Pereira <yuran.pereira@...mail.com>
> ---
>  kernel/trace/ftrace.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 8de8bec5f366..70217ee97322 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -4233,12 +4233,12 @@ static int
>  add_rec_by_index(struct ftrace_hash *hash, struct ftrace_glob *func_g,
>  		 int clear_filter)
>  {
> -	long index = simple_strtoul(func_g->search, NULL, 0);
> +	long index;
>  	struct ftrace_page *pg;
>  	struct dyn_ftrace *rec;
>  
>  	/* The index starts at 1 */
> -	if (--index < 0)
> +	if (kstrtoul(func_g->search, 0, &index) || --index < 0)
>  		return 0;
>  
>  	do_for_each_ftrace_rec(pg, rec) {
> @@ -5810,9 +5810,8 @@ __setup("ftrace_graph_notrace=", set_graph_notrace_function);
>  
>  static int __init set_graph_max_depth_function(char *str)
>  {
> -	if (!str)
> +	if (!str || kstrtouint(str, 0, &fgraph_max_depth))
>  		return 0;
> -	fgraph_max_depth = simple_strtoul(str, NULL, 0);
>  	return 1;
>  }
>  __setup("ftrace_graph_max_depth=", set_graph_max_depth_function);
> -- 
> 2.25.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>