On Mon, Jan 31, 2022 at 04:34:13PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> Most callers of public_key_verify_signature(), including most indirect
> callers via verify_signature() as well as pkcs7_verify_sig_chain(),
> don't check that public_key_signature::pkey_algo matches
> public_key::pkey_algo. These should always match. However, a malicious
> signature could intentionally declare an unintended algorithm. It is
> essential that such signatures be rejected outright, or that the
> algorithm of the *key* be used -- not the algorithm of the signature as
> that would allow attackers to choose the algorithm used.
>
> Currently, public_key_verify_signature() correctly uses the key's
> algorithm when deciding which akcipher to allocate. That's good.
> However, it uses the signature's algorithm when deciding whether to do
> the first step of SM2, which is incorrect. Also, v4.19 and older
> kernels used the signature's algorithm for the entire process.
>
> Prevent such errors by making public_key_verify_signature() enforce that
> the signature's algorithm matches the key's algorithm.
>
> Also remove two checks of this done by callers, which are now redundant.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> ---
> crypto/asymmetric_keys/pkcs7_verify.c | 6 ------
> crypto/asymmetric_keys/public_key.c | 15 +++++++++++++++
> crypto/asymmetric_keys/x509_public_key.c | 6 ------
> 3 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
> index 0b4d07aa88111..f94a1d1ad3a6c 100644
> --- a/crypto/asymmetric_keys/pkcs7_verify.c
> +++ b/crypto/asymmetric_keys/pkcs7_verify.c
> @@ -174,12 +174,6 @@ static int pkcs7_find_key(struct pkcs7_message *pkcs7,
> pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
> sinfo->index, certix);
>
> - if (strcmp(x509->pub->pkey_algo, sinfo->sig->pkey_algo) != 0) {
> - pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
> - sinfo->index);
> - continue;
> - }
> -
> sinfo->signer = x509;
> return 0;
> }
> diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
> index 4fefb219bfdc8..aba7113d86c76 100644
> --- a/crypto/asymmetric_keys/public_key.c
> +++ b/crypto/asymmetric_keys/public_key.c
> @@ -325,6 +325,21 @@ int public_key_verify_signature(const struct public_key *pkey,
> BUG_ON(!sig);
> BUG_ON(!sig->s);
>
> + /*
> + * The signature's claimed public key algorithm *must* match the key's
> + * actual public key algorithm.
> + *
> + * Small exception: ECDSA signatures don't specify the curve, but ECDSA
> + * keys do. So the strings can mismatch slightly in that case:
> + * "ecdsa-nist-*" for the key, but "ecdsa" for the signature.
> + */
> + if (!sig->pkey_algo)
> + return -EINVAL;
> + if (strcmp(pkey->pkey_algo, sig->pkey_algo) != 0 &&
> + (strncmp(pkey->pkey_algo, "ecdsa-", 6) != 0 ||
> + strcmp(sig->pkey_algo, "ecdsa") != 0))
> + return -EKEYREJECTED;
> +
> ret = software_key_determine_akcipher(sig->encoding,
> sig->hash_algo,
> pkey, alg_name);
> diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
> index fe14cae115b51..71cc1738fbfd2 100644
> --- a/crypto/asymmetric_keys/x509_public_key.c
> +++ b/crypto/asymmetric_keys/x509_public_key.c
> @@ -128,12 +128,6 @@ int x509_check_for_self_signed(struct x509_certificate *cert)
> goto out;
> }
>
> - ret = -EKEYREJECTED;
> - if (strcmp(cert->pub->pkey_algo, cert->sig->pkey_algo) != 0 &&
> - (strncmp(cert->pub->pkey_algo, "ecdsa-", 6) != 0 ||
> - strcmp(cert->sig->pkey_algo, "ecdsa") != 0))
> - goto out;
> -
> ret = public_key_verify_signature(cert->pub, cert->sig);
> if (ret < 0) {
> if (ret == -ENOPKG) {
> --
> 2.35.1
>
Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
David, do you want to pick this?
BR, Jarkko
