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

[Andrei Borzenkov]

29.03.2016 22:02, Ignat Korchagin пишет:
> 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.
> 
> diff --git a/grub-core/commands/verify.c b/grub-core/commands/verify.c
> index 166d0aa..dde37c4 100644
> --- a/grub-core/commands/verify.c
> +++ b/grub-core/commands/verify.c
> @@ -532,33 +532,15 @@
>  
>      hash->write (context, &v, sizeof (v));
>      hash->write (context, &v4, sizeof (v4));
> -    while (rem)
> -      {
> -     r = grub_file_read (sig, readbuf,
> -                         rem < READBUF_SIZE ? rem : READBUF_SIZE);
> -     if (r < 0)
> -       goto fail;
> -     if (r == 0)
> -       break;
> -     hash->write (context, readbuf, r);
> -     rem -= r;
> -      }
> -    hash->write (context, &v, sizeof (v));
> -    s = 0xff;
> -    hash->write (context, &s, sizeof (s));
> -    hash->write (context, &headlen, sizeof (headlen));
> -    r = grub_file_read (sig, &unhashed_sub, sizeof (unhashed_sub));
> -    if (r != sizeof (unhashed_sub))
> +    if (rem > READBUF_SIZE)
> +      goto fail;

This changes behavior. It accepted hashed subpackets of arbitrary length
before. If this was not appropriate, please explain why.

> +    r = grub_file_read (sig, readbuf, rem);
> +    if (r != rem)
>        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)
> @@ -581,6 +563,46 @@
>           keyid = grub_get_unaligned64 (ptr + 1);
>       }
>      }
> +    hash->write (context, readbuf, r);
> +    hash->write (context, &v, sizeof (v));
> +    s = 0xff;
> +    hash->write (context, &s, sizeof (s));
> +    hash->write (context, &headlen, sizeof (headlen));
> +    r = grub_file_read (sig, &unhashed_sub, sizeof (unhashed_sub));
> +    if (r != sizeof (unhashed_sub))
> +      goto fail;
> +    if (keyid == 0)
> +      {
> +        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);
> +       }
> +      }
>  
>      hash->final (context);
>  
> 
> 
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