linux-hardening - Re: [PATCH] selinux: Annotate struct sidtab_str_cache with __counted

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Date:   Fri, 18 Aug 2023 12:25:12 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Ondrej Mosnacek <omosnace@...hat.com>, selinux@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        "GONG, Ruiqi" <gongruiqi1@...wei.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] selinux: Annotate struct sidtab_str_cache with __counted_by

On Thu, Aug 17, 2023 at 4:22 PM Kees Cook <keescook@...omium.org> wrote:
>
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> As found with Coccinelle[1], add __counted_by for struct sidtab_str_cache.
>
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
>
> Cc: Paul Moore <paul@...l-moore.com>
> Cc: Stephen Smalley <stephen.smalley.work@...il.com>
> Cc: Eric Paris <eparis@...isplace.org>
> Cc: Ondrej Mosnacek <omosnace@...hat.com>
> Cc: selinux@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  security/selinux/ss/sidtab.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

This also looks good to me, but similarly to the audit patch, since we
are at -rc6 I'm going to wait to merge this until after the merge
window.  I'll send a follow up email once it's merged.

Thanks.

> diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
> index d8ead463b8df..732fd8e22a12 100644
> --- a/security/selinux/ss/sidtab.c
> +++ b/security/selinux/ss/sidtab.c
> @@ -25,7 +25,7 @@ struct sidtab_str_cache {
>         struct list_head lru_member;
>         struct sidtab_entry *parent;
>         u32 len;
> -       char str[];
> +       char str[] __counted_by(len);
>  };
>
>  #define index_to_sid(index) ((index) + SECINITSID_NUM + 1)
> --
> 2.34.1

-- 
paul-moore.com