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List:       linux-keyrings
Subject:    Re: [PATCH v4] KEYS: encrypted: fix key instantiation with user-provided data
From:       Nikolaus Voss <nv () vosn ! de>
Date:       2022-10-23 7:52:20
Message-ID: c0562c3-aa31-098-4473-ac8818fdc5a () vosn ! de
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On Sun, 23 Oct 2022, Jarkko Sakkinen wrote:
> On Sun, Oct 23, 2022 at 08:18:58AM +0300, Jarkko Sakkinen wrote:
> > On Thu, Oct 13, 2022 at 08:39:58AM +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
> > > 
> > > It is encouraged to switch to a new key because the effective key size
> > > of the old keys is only half of the specified size.
> > > 
> > > 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 <stable@kernel.org>
> > > Link: https://lore.kernel.org/ltp/20221006081709.92303897@mail.steuer-voss.de/
> > > Signed-off-by: Nikolaus Voss <nikolaus.voss@haag-streit.com>
> > > ---
> > > Changes
> > > =======
> > > v4: - fixed link
> > > v3: - use generated random key in example, reformat commit message
> > > v2: - clarify commit message, add example to recover old/broken keys
> > > - improve example in Documentation/security/keys/trusted-encrypted.rst
> > > - add link to ltp patch
> > > 
> > > Documentation/security/keys/trusted-encrypted.rst | 3 ++-
> > > security/keys/encrypted-keys/encrypted.c          | 6 +++---
> > > 2 files changed, 5 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/Documentation/security/keys/trusted-encrypted.rst \
> > > b/Documentation/security/keys/trusted-encrypted.rst index \
> > >                 0bfb4c339748..9bc9db8ec651 100644
> > > --- a/Documentation/security/keys/trusted-encrypted.rst
> > > +++ b/Documentation/security/keys/trusted-encrypted.rst
> > > @@ -350,7 +350,8 @@ Load an encrypted key "evm" from saved blob::
> > > 
> > > Instantiate an encrypted key "evm" using user-provided decrypted data::
> > > 
> > > -    $ keyctl add encrypted evm "new default user:kmk 32 `cat \
> > > evm_decrypted_data.blob`" @u +    $ evmkey=$(dd if=/dev/urandom bs=1 count=32 | \
> > > xxd -c32 -p) +    $ keyctl add encrypted evm "new default user:kmk 32 $evmkey" \
> > > @u 794890253
> > > 
> > > $ keyctl print 794890253
> > > diff --git a/security/keys/encrypted-keys/encrypted.c \
> > > b/security/keys/encrypted-keys/encrypted.c index e05cfc2e49ae..1e313982af02 \
> > >                 100644
> > > --- a/security/keys/encrypted-keys/encrypted.c
> > > +++ b/security/keys/encrypted-keys/encrypted.c
> > > @@ -627,7 +627,7 @@ static struct encrypted_key_payload \
> > > *encrypted_key_alloc(struct key *key,  pr_err("encrypted key: instantiation of \
> > > keys using provided decrypted data is disabled since CONFIG_USER_DECRYPTED_DATA \
> > > is set to false\n");  return ERR_PTR(-EINVAL);
> > > 		}
> > > -		if (strlen(decrypted_data) != decrypted_datalen) {
> > > +		if (strlen(decrypted_data) != decrypted_datalen * 2) {
> > > 			pr_err("encrypted key: decrypted data provided does not match decrypted data \
> > > length provided\n");  return ERR_PTR(-EINVAL);
> > > 		}
> > > @@ -791,8 +791,8 @@ static int encrypted_init(struct encrypted_key_payload \
> > > *epayload,  ret = encrypted_key_decrypt(epayload, format, hex_encoded_iv);
> > > 	} else if (decrypted_data) {
> > > 		get_random_bytes(epayload->iv, ivsize);
> > > -		memcpy(epayload->decrypted_data, decrypted_data,
> > > -				   epayload->decrypted_datalen);
> > > +		ret = hex2bin(epayload->decrypted_data, decrypted_data,
> > > +			      epayload->decrypted_datalen);
> > > 	} else {
> > > 		get_random_bytes(epayload->iv, ivsize);
> > > 		get_random_bytes(epayload->decrypted_data, epayload->decrypted_datalen);
> > > --
> > > 2.34.1
> > > 
> > 
> > 
> > Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> > 
> > Unless there is opposing views, I can pick this.
> 
> Actually, taking this back: please fix the checkpatch warnings first.

I fixed the warnings in v5, Mimi took this already.

Niko


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