On Wed, Oct 19, 2022 at 06:38:20PM +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@xxxxxxxxxx
> Link: https://lore.kernel.org/ltp/20221006081709.92303897@xxxxxxxxxxxxxxxxxxx/
> Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> Signed-off-by: Nikolaus Voss <nikolaus.voss@xxxxxxxxxxxxxxx>
> ---
> Changes
> =======
> v6: - fix checkpatch warnings
> v5: - explain security issue in commit message, add Reviewd-by
> v4: - change "Link:" address
> 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
>
Did you check that this passes "checkpatch.pl --strict"?
Your earlier version did not.
BR, Jarkko
