[Pkg-cryptsetup-devel] Bug#381973: cryptsetup segfaults with unsupported keysize

[Jonas Meurer]

Hello Clemens,

Debian bugreport #381973 reports that cryptsetup segfaults when an
incompatible keysize is given as an option.

Later David Härdeman analyzed the following:

> During "cryptsetup luksOpen" with the previously set 448 bit (56 byte)
> key, we'll have the following call chain:
>
> main -> action_luksOpen -> crypt_job -> __crypt_luks_open ->
> LUKS_open_any_key -> LUKS_open_key -> AF_merge
> 
> AF_merge is being called as:
> AF_merge(AfKey,mk->key,mk->keyLength,hdr->keyblock[keyIndex].stripes);
> 
> mk->keyLength is here (correctly) set to 56, and mk->key is a statically
> allocated 32 byte buffer (defined as part of struct luks_masterkey in
> luks.h).
> 
> This will lead the last call to XORblock in AF_merge to scribble 56 - 32
> bytes outside that buffer, thus corrupting the stack and leading to
> interesting crashes in unrelated places later.

The simplest solution would be to check whether mk->keyLength is a
multible of eigth and exit with an error message otherwise, correct?

or would that break something?
If not, it would be rather easy to fix, and i would love to see it
fixed in debian etch.

...
 jonas