Re: [PATCH] verify: search keyid in hashed signature subpackets (repost)

[Daniel Kiper]

On Fri, Nov 18, 2016 at 12:00:08PM +0000, Ignat Korchagin wrote:
> Reposting this, as requested by Daniel and rebasing on current tree.
>
> Currently GRUB2 verify logic searches PGP keyid only in unhashed subpackets 
> of PGP signature packet. As a result, signatures generated with GoLang 
> openpgp package (https://godoc.org/golang.org/x/crypto/openpgp) could not be 
> verified, because this package puts keyid in hashed subpackets and GRUB code 
> never initializes the keyid variable, therefore is not able to find 
> "verification key" with id 0x0.
>
> Signed-off-by: Ignat Korchagin <address@hidden>
> ---
>  grub-core/commands/verify.c | 115 
> +++++++++++++++++++++++++++++---------------
>  1 file changed, 76 insertions(+), 39 deletions(-)
>
> diff --git a/grub-core/commands/verify.c b/grub-core/commands/verify.c
> index 67cb1c7..1b628b2 100644
> --- a/grub-core/commands/verify.c
> +++ b/grub-core/commands/verify.c
> @@ -445,6 +445,38 @@ rsa_pad (gcry_mpi_t *hmpi, grub_uint8_t *hval,
>    return ret;
>  }
>
> +static grub_uint64_t
> +grub_subpacket_keyid_search (const grub_uint8_t * sub, grub_ssize_t sub_len)
> +{
> +  const grub_uint8_t *ptr;
> +  grub_uint32_t l;
> +  grub_uint64_t keyid = 0;
> +
> +  for (ptr = sub; ptr < sub + sub_len; ptr += l)
> +    {
> +      if (*ptr < 192)

Please define some constants and use them properly...

> +        l = *ptr++;
> +      else if (*ptr < 255)

Ditto.

> +        {
> +          if (ptr + 1 >= sub + sub_len)
> +            break;
> +          l = (((ptr[0] & ~192) << GRUB_CHAR_BIT) | ptr[1]) + 192;

Ditto.

> +          ptr += 2;

Ditto and below...

> +        }
> +      else
> +        {
> +          if (ptr + 5 >= sub + sub_len)
> +            break;
> +          l = grub_be_to_cpu32 (grub_get_unaligned32 (ptr + 1));
> +          ptr += 5;
> +        }
> +      if (*ptr == 0x10 && l >= 8)
> +        keyid = grub_get_unaligned64 (ptr + 1);
> +    }
> +
> +  return keyid;
> +}
> +
>  static grub_err_t
>  grub_verify_signature_real (char *buf, grub_size_t size,
>                           grub_file_t f, grub_file_t sig,
> @@ -529,20 +561,31 @@ grub_verify_signature_real (char *buf, grub_size_t size,
>           break;
>         hash->write (context, readbuf, r);
>       }
> +    grub_free (readbuf);
> +
> +    readbuf = grub_malloc (rem);

grub_zalloc()?

> +    if (!readbuf)
> +      goto fail;
>
>      hash->write (context, &v, sizeof (v));
>      hash->write (context, &v4, sizeof (v4));
> -    while (rem)
> +
> +    r = 0;
> +    while (r < rem)
>        {
> -     r = grub_file_read (sig, readbuf,
> -                         rem < READBUF_SIZE ? rem : READBUF_SIZE);
> -     if (r < 0)
> -       goto fail;
> -     if (r == 0)
> +        grub_ssize_t rr = grub_file_read (sig, readbuf + r, rem - r);
> +        if (rr < 0)
> +          goto fail;
> +        if (rr == 0)
>         break;
> -     hash->write (context, readbuf, r);
> -     rem -= r;
> +        r += rr;
>        }
> +    if (r != rem)
> +      goto fail;
> +    hash->write (context, readbuf, rem);
> +    keyid = grub_subpacket_keyid_search (readbuf, rem);
> +    grub_free (readbuf);
> +
>      hash->write (context, &v, sizeof (v));
>      s = 0xff;
>      hash->write (context, &s, sizeof (s));
> @@ -550,40 +593,34 @@ grub_verify_signature_real (char *buf, grub_size_t size,
>      r = grub_file_read (sig, &unhashed_sub, sizeof (unhashed_sub));
>      if (r != sizeof (unhashed_sub))
>        goto fail;
> -    {
> -      grub_uint8_t *ptr;
> -      grub_uint32_t l;
> -      rem = grub_be_to_cpu16 (unhashed_sub);
> -      if (rem > READBUF_SIZE)
> -     goto fail;
> -      r = grub_file_read (sig, readbuf, rem);
> -      if (r != rem)
> -     goto fail;
> -      for (ptr = readbuf; ptr < readbuf + rem; ptr += l)
> -     {
> -       if (*ptr < 192)
> -         l = *ptr++;
> -       else if (*ptr < 255)
> -         {
> -           if (ptr + 1 >= readbuf + rem)
> -             break;
> -           l = (((ptr[0] & ~192) << GRUB_CHAR_BIT) | ptr[1]) + 192;
> -           ptr += 2;
> -         }
> -       else
> -         {
> -           if (ptr + 5 >= readbuf + rem)
> -             break;
> -           l = grub_be_to_cpu32 (grub_get_unaligned32 (ptr + 1));
> -           ptr += 5;
> -         }
> -       if (*ptr == 0x10 && l >= 8)
> -         keyid = grub_get_unaligned64 (ptr + 1);
> -     }
> -    }
> +    rem = grub_be_to_cpu16 (unhashed_sub);
> +    readbuf = grub_malloc (rem);

grub_zalloc()?

Daniel