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Message-ID: <CAGXu5jJ=46_1DiWg=0aKzOo1+kxL9vemLFi11brn-+iY6cgZMw@mail.gmail.com>
Date: Mon, 26 Mar 2018 16:16:23 -0700
From: Kees Cook <keescook@...omium.org>
To: Salvatore Mesoraca <s.mesoraca16@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>, Ingo Molnar <mingo@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] ftrace: drop a VLA in module_exists()
On Tue, Mar 13, 2018 at 12:51 PM, Salvatore Mesoraca
<s.mesoraca16@...il.com> wrote:
> Avoid a VLA[1] by using a real constant expression instead of a variable.
> The compiler should be able to optimize the original code and avoid using
> an actual VLA. Anyway this change is useful because it will avoid a false
> positive with -Wvla, it might also help the compiler generating better
> code.
>
> [1] https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Salvatore Mesoraca <s.mesoraca16@...il.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 eac9ce2..adebb92 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -3902,14 +3902,13 @@ static bool module_exists(const char *module)
> {
> /* All modules have the symbol __this_module */
> const char this_mod[] = "__this_module";
> - const int modname_size = MAX_PARAM_PREFIX_LEN + sizeof(this_mod) + 1;
> - char modname[modname_size + 1];
> + char modname[MAX_PARAM_PREFIX_LEN + sizeof(this_mod) + 1];
Actually, I think this needs to be "+ 2" (":" and NULL).
> unsigned long val;
> int n;
>
> - n = snprintf(modname, modname_size + 1, "%s:%s", module, this_mod);
> + n = snprintf(modname, sizeof(modname), "%s:%s", module, this_mod);
>
> - if (n > modname_size)
> + if (n > sizeof(modname) - 1)
> return false;
>
> val = module_kallsyms_lookup_name(modname);
Otherwise, looks good!
-Kees
--
Kees Cook
Pixel Security
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