linux-kernel - Re: [PATCH] modpost: fix removing numeric suffixes

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Date:   Fri, 27 May 2022 16:06:35 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Alexander Lobakin <alexandr.lobakin@...el.com>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Michal Nazarewicz <mina86@...a86.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] modpost: fix removing numeric suffixes

On Wed, May 25, 2022 at 12:28 AM Alexander Lobakin
<alexandr.lobakin@...el.com> wrote:
>
> With the `-z unique-symbol` linker flag or any similar mechanism,
> it is possible to trigger the following:
>
> ERROR: modpost: "param_set_uint.0" [vmlinux] is a static EXPORT_SYMBOL
>
> The reason is that for now the condition from remove_dot():
>
> if (m && (s[n + m] == '.' || s[n + m] == 0))
>
> which was designed to test if it's a dot or a '\0' after the suffix
> is never satisfied.
> This is due to that `s[n + m]` always points to the last digit of a
> numeric suffix, not on the symbol next to it (from a custom debug
> print added to modpost):
>
> param_set_uint.0, s[n + m] is '0', s[n + m + 1] is '\0'
>
> So it's off-by-one and was like that since 2014.
>
> Fix this for the sake of any potential upcoming features, but don't
> bother stable-backporting, as it's well hidden -- apart from that
> LD flag, it can be triggered only with GCC LTO which never landed
> upstream.
>
> Fixes: fcd38ed0ff26 ("scripts: modpost: fix compilation warning")
> Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> ---


Applied to linux-kbuild.
Thanks.



>  scripts/mod/modpost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 6f5c605ab0fb..fd04ba057490 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1905,7 +1905,7 @@ static char *remove_dot(char *s)
>
>         if (n && s[n]) {
>                 size_t m = strspn(s + n + 1, "0123456789");
> -               if (m && (s[n + m] == '.' || s[n + m] == 0))
> +               if (m && (s[n + m + 1] == '.' || s[n + m + 1] == 0))
>                         s[n] = 0;
>         }
>         return s;
> --
> 2.36.1
>


-- 
Best Regards
Masahiro Yamada