linux-kernel - Re: [PATCH 1/3] modpost: add array range check to sec

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Date:   Tue, 2 Aug 2022 10:55:39 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] modpost: add array range check to sec_name()

On Sat, Jul 30, 2022 at 10:37 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> The section index is always positive, so the argunent, secindex, should
> be unsigned.
>
> Also, inserted the array range check.
>
> If sym->st_shndx is a special section index (between SHN_LORESERVE and
> SHN_HIRESERVE), there is no corresponding section header.
>
> For example, if a symbol specifies an absolute value, sym->st_shndx is
> SHN_ABS (=0xfff1).
>
> The current users do not cause the out-of-range access of
> info->sechddrs[], but it is better to avoid such a pitfall.
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

I don't mind adding this check; though if it's anomalous I think we
could also just print to stderr and abort.

I would prefer Elf_Sym over unsigned int though.  WDYT?

> ---
>
>  scripts/mod/modpost.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 08411fff3e17..148b38699889 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -336,8 +336,16 @@ static const char *sech_name(const struct elf_info *info, Elf_Shdr *sechdr)
>                                       sechdr->sh_name);
>  }
>
> -static const char *sec_name(const struct elf_info *info, int secindex)
> +static const char *sec_name(const struct elf_info *info, unsigned int secindex)
>  {
> +       /*
> +        * If sym->st_shndx is a special section index, there is no
> +        * corresponding section header.
> +        * Return "" if the index is out of range of info->sechdrs[] array.
> +        */
> +       if (secindex >= info->num_sections)
> +               return "";
> +
>         return sech_name(info, &info->sechdrs[secindex]);
>  }
>
> --
> 2.34.1
>


-- 
Thanks,
~Nick Desaulniers