[PATCH] smbios: Fix table when no string is present

[Simon Glass]

Hi Matthias,

On Thu, 18 Mar 2021 at 00:30, <matthias.bgg at kernel.org> wrote:
>
> From: Matthias Brugger <mbrugger at suse.com>
>
> When no string is present in a table, next_ptr points to the same
> location as eos. When calculating the string table length, we would only
> reserve one \0. By spec a SMBIOS table has to end with two \0\0 when no
> strings a present.
>
> Signed-off-by: Matthias Brugger <mbrugger at suse.com>
>
> ---
>
>  lib/smbios.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

There is a bug here but I don't think this is right fix. I remember
worrying about this, making the same change as you did, reverting it
and then forgetting about it :-( It has no tests.

You are effectively changing the definition of next_ptr here:

 * @next_ptr: pointer to the start of the next string to be added. When the
 * table is not empty, this points to the byte after the \0 of the
 * previous string.

(there is a typo in that in the code)

I think that breaks adding new strings.

Can you instead change smbios_string_table_len() to add 2?

>
> diff --git a/lib/smbios.c b/lib/smbios.c
> index 7d463c84a9..d21d37cdac 100644
> --- a/lib/smbios.c
> +++ b/lib/smbios.c
> @@ -153,7 +153,7 @@ static int smbios_add_prop(struct smbios_ctx *ctx, const char *prop)
>  static void smbios_set_eos(struct smbios_ctx *ctx, char *eos)
>  {
>         ctx->eos = eos;
> -       ctx->next_ptr = eos;
> +       ctx->next_ptr = eos + 1;
>         ctx->last_str = NULL;
>  }
>
> --
> 2.30.2
>

Regards,
Simon