On Tue, 2022-09-20 at 18:23 +0200, Nikolaus Voss wrote:
> On Tue, 20 Sep 2022, Mimi Zohar wrote:
> > On Fri, 2022-09-16 at 07:45 +0200, Nikolaus Voss wrote:
> >> Commit cd3bc044af48 ("KEYS: encrypted: Instantiate key with user-provided
> >> decrypted data") added key instantiation with user provided decrypted data.
> >> The user data is hex-ascii-encoded but was just memcpy'ed to the binary buffer.
> >> Fix this to use hex2bin instead.
> >
> > Thanks, Nikolaus. We iterated a number of times over what would be the
> > safest userspace input. One of the last changes was that the key data
> > should be hex-ascii-encoded. Unfortunately, the LTP
> > testcases/kernel/syscalls/keyctl09.c example isn't hex-ascii-encoded
> > and the example in Documentation/security/keys/trusted-encrypted.rst
> > just cat's a file. Both expect the length to be the length of the
> > userspace provided data. With this patch, when hex2bin() fails, there
> > is no explanation.
>
> That's true. But it's true for all occurrences of hex2bin() in this file.
> I could pr_err() an explanation, improve the trusted-encrypted.rst example
> and respin the patch. Should I, or do you have another suggestion?
> I wasn't aware of keyctl09.c, but quickly looking into it, the user data
> _is_ hex-ascii-encoded, only the length is "wrong": Imho, the specified
> length should be the binary length as this is consistent with key-length
> specs in other cases (e.g. when loading the key from a blob).
> keyctl09.c could be easy to fix, if only the length is modified. Should
> I propose a patch? What is the correct/appropriate workflow there?
I'm concerned that this change breaks existing encrypted keys created
with user-provided data. Otherwise I'm fine with your suggestion.
The LTP example decrypted data length is 32, but the minimum decrypted
data size is 20. So it's a bit more than just changing the LTP
decrypted data size. The modified LTP test should work on kernels
with and without this patch.
--
thanks,
Mimi
