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Date: Sun, 30 Dec 2012 15:07:07 +0530
From: Dhiru Kholia <>
Subject: Re: Rejecting hashes in valid() due to memory allocation failures?

On Sun, Dec 30, 2012 at 1:39 PM, Frank Dittrich
<> wrote:
> Making sure to only accept valid hashes is certainly a good thing.
> But I wonder if changes like this one (just the most recent I found, I'm
> sure there are more) are OK:
> src/pbkdf2-hmac-sha512_fmt_plug.c
> +  if (!(ctcopy = strdup(ciphertext)))
> +    return 0;
> In such a case, the hash could be valid, but it gets treated as if it
> were invalid.
> 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
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?


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