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Date: Sun, 30 Dec 2012 11:25:46 +0100
From: Frank Dittrich <>
Subject: Re: Rejecting hashes in valid() due to memory allocation

On 12/30/2012 10:37 AM, Dhiru Kholia wrote:
> On Sun, Dec 30, 2012 at 1:39 PM, Frank Dittrich <> wrote:
>> How unlikely is it that a memory allocation failure occurs when trying
>> to crack a huge number of passwords?
>> (This could also be caused by strict ulimit settings.)
>> IMHO, In such a case we shouldn't silently drop valid hashes as if they
>> were invalid, but instead at least print some kind of error message.
>> (May be even change the interface and allow a negative return value in
>> valid(), to signal that there is a more general problem, so that we
>> don't get thousands of error messages for memory allocation failures...)
> diff --git a/src/pbkdf2-hmac-sha512_fmt_plug.c
> b/src/pbkdf2-hmac-sha512_fmt_plug.c
> index e6471b9..f560195 100644
> --- a/src/pbkdf2-hmac-sha512_fmt_plug.c
> +++ b/src/pbkdf2-hmac-sha512_fmt_plug.c
> @@ -90,8 +90,10 @@ static int valid(char *ciphertext, struct fmt_main *self)
>         if (strncmp(ciphertext, FORMAT_TAG, strlen(FORMAT_TAG)))
>                 return 0;
> -       if (!(ctcopy = strdup(ciphertext)))
> +       if (!(ctcopy = strdup(ciphertext))) {
> +               fprintf(stderr, "Memory allocation failed in %s,
> unable to check if hash is valid!", FORMAT_LABEL);
>                 return 0;
> +       }
>         keeptr = ctcopy;
>         ctcopy += strlen(FORMAT_TAG);
>         if (!(ptr = strtok(ctcopy, ".")))
> Does this look OK?

Actually, I just wanted to raise general awareness of a possible issue.
I doubt that you'll ever try to crack so many GRUB2 hashes that you run
into this issue.
(It is also unlikely that many ciphertexts of other formats start with

But for formats where this could happen, I don't think one error message
per memory allocation failure is a good idea.


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