Re: [PATCH v6] KEYS: encrypted: fix key instantiation with user-provided data

[Jarkko Sakkinen <jarkko@kernel.org>]

On Wed, Oct 19, 2022 at 05:28:23PM -0400, Mimi Zohar wrote:
> On Wed, 2022-10-19 at 18:38 +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.
> > 
> > Old keys created from user provided decrypted data saved with "keyctl
> > pipe" are still valid, however if the key is recreated from decrypted
> > data the old key must be converted to the correct format. This can be
> > done with a small shell script, e.g.:
> > 
> > BROKENKEY=abcdefABCDEF1234567890aaaaaaaaaa
> > NEWKEY=$(echo -ne $BROKENKEY | xxd -p -c32)
> > keyctl add user masterkey "$(cat masterkey.bin)" @u
> > keyctl add encrypted testkey "new user:masterkey 32 $NEWKEY" @u
> > 
> > However, NEWKEY is still broken: If for BROKENKEY 32 bytes were
> > specified, a brute force attacker knowing the key properties would only
> > need to try at most 2^(16*8) keys, as if the key was only 16 bytes long.
> > 
> > The security issue is a result of the combination of limiting the input
> > range to hex-ascii and using memcpy() instead of hex2bin(). It could
> > have been fixed either by allowing binary input or using hex2bin() (and
> > doubling the ascii input key length). This patch implements the latter.
> > 
> > The corresponding test for the Linux Test Project ltp has also been
> > fixed (see link below).
> > 
> > Fixes: cd3bc044af48 ("KEYS: encrypted: Instantiate key with user-provided decrypted data")
> > Cc: stable@kernel.org
> > Link: https://lore.kernel.org/ltp/20221006081709.92303897@mail.steuer-voss.de/
> > Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
> > Signed-off-by: Nikolaus Voss <nikolaus.voss@haag-streit.com>
> 
> Thanks!  This patch is now queued in next-integrity/next-integrity-
> testing.

Did you check the checkpatch.pl because earlier versions did not pass.

BR, Jarkko