KEYS: asymmetric: enforce that sig algo matches key algo

commit 2abc9c246e0548e52985b10440c9ea3e9f65f793 upstream.

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 (if given) matches the key's algorithm.

Also remove two checks of this done by callers, which are now redundant.

Cc: stable@vger.kernel.org
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Tested-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Vitaly Chikunov <vt@altlinux.org>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
index 0b4d07aa88111e332d16faeb2f97d8b594585741..f94a1d1ad3a6cd71405f2236850d5f6668b29b3f 100644 (file)
--- 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 4fefb219bfdc86318f33b822eef7bc8214a2a106..e36213945686f6fb375f2fc4def87754c9fb7b0e 100644 (file)
--- 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);
 
+       /*
+        * If the signature specifies a public key algorithm, it *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) {
+               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 3d45161b271a48f4a508a0dd3d9a981e6f7f15dd..7fd56df8b91944cd586e361eca840dac4110c1f9 100644 (file)
--- 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) {