Re: [Bug-tar] 'BZh[1-9]' file in v7 format archive confuses GNU tar

[Michał Górny]

On Wed, 2018-11-28 at 14:32 +0200, Sergey Poznyakoff wrote:
> Michał Górny <address@hidden> ha escrit:
> 
> > FWICS the problem is that one of the checksum variants evaluates to zero
> > and tar is rather lax on accepting null checksum string (with trailing
> > garbage) as zero.
> 
> That's easy to fix (see the attached patch). I'm not quite convinced
> that it doesn't break backward compatibility though (can such headers be
> found in some old archives?)

Well, I was thinking of applying the change only to the heuristic used
to detect compression, i.e. still being lax on accepting tarballs that
don't look like they're compressed.

> diff --git a/src/buffer.c b/src/buffer.c
> index ddb63cc..5632aee 100644
> --- a/src/buffer.c
> +++ b/src/buffer.c
> @@ -406,10 +406,6 @@ check_compressed_archive (bool *pshort)
>    read_full_records = sfr;
>  
>    if (record_start != record_end /* no files smaller than BLOCKSIZE */
> -      && (strcmp (record_start->header.magic, TMAGIC) == 0
> -          || strcmp (record_start->buffer + offsetof (struct posix_header,
> -                                                      magic),
> -                     OLDGNU_MAGIC) == 0)
>        && tar_checksum (record_start, true) == HEADER_SUCCESS)
>      /* Probably a valid header */
>      return ct_tar;
> diff --git a/src/list.c b/src/list.c
> index ba9c306..0dacbb7 100644
> --- a/src/list.c
> +++ b/src/list.c
> @@ -892,6 +892,11 @@ from_header (char const *where0, size_t digs, char const 
> *type,
>       value = -value;
>      }
>  
> +  /* Skip consecutive \0's. This ensures the test below will catch eventual
> +     trailing garbage */
> +  while (where < lim && !*where)
> +    where++;

Does this fail if checksum consists solely of NULs without a single
octal digit?

> +
>    if (where != lim && *where && !isspace ((unsigned char) *where))
>      {
>        if (type)

-- 
Best regards,
Michał Górny

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