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

[Andrei Borzenkov <arvidjaar@gmail.com>]

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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