X.509: Support parse long form of length octets in Authority Key Identifier
Chun-Yi Lee [Mon, 22 Apr 2013 01:26:55 +0000 (10:26 +0930)]
Per X.509 spec in 4.2.1.1 section, the structure of Authority Key
Identifier Extension is:

   AuthorityKeyIdentifier ::= SEQUENCE {
      keyIdentifier             [0] KeyIdentifier           OPTIONAL,
      authorityCertIssuer       [1] GeneralNames            OPTIONAL,
      authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL  }

   KeyIdentifier ::= OCTET STRING

When a certificate also provides
authorityCertIssuer and authorityCertSerialNumber then the length of
AuthorityKeyIdentifier SEQUENCE is likely to long form format.
e.g.
   The example certificate demos/tunala/A-server.pem in openssl source:

X509v3 Authority Key Identifier:
    keyid:49:FB:45:72:12:C4:CC:E1:45:A1:D3:08:9E:95:C4:2C:6D:55:3F:17
    DirName:/C=NZ/L=Wellington/O=Really Irresponsible Authorisation Authority (RIAA)/OU=Cert-stamping/CN=Jackov al-Trades/emailAddress=none@fake.domain
    serial:00

Current parsing rule of OID_authorityKeyIdentifier only take care the
short form format, it causes load certificate to modsign_keyring fail:

[   12.061147] X.509: Extension: 47
[   12.075121] MODSIGN: Problem loading in-kernel X.509 certificate (-74)

So, this patch add the parsing rule for support long form format against
Authority Key Identifier.

v3:
Changed the size check in "Short Form length" case, we allow v[3] smaller
then (vlen - 4) because authorityCertIssuer and authorityCertSerialNumber
are also possible attach in AuthorityKeyIdentifier sequence.

v2:
 - Removed comma from author's name.
 - Moved 'Short Form length' comment inside the if-body.
 - Changed the type of sub to size_t.
 - Use ASN1_INDEFINITE_LENGTH rather than writing 0x80 and 127.
 - Moved the key_len's value assignment before alter v.
 - Fixed the typo of octets.
 - Add 2 to v before entering the loop for calculate the length.
 - Removed the comment of check vlen.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Josh Boyer <jwboyer@redhat.com>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Chun-Yi Lee <jlee@suse.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

crypto/asymmetric_keys/x509_cert_parser.c

index 7fabc4c..facbf26 100644 (file)
@@ -373,6 +373,9 @@ int rsa_extract_mpi(void *context, size_t hdrlen,
        return 0;
 }
 
+/* The keyIdentifier in AuthorityKeyIdentifier SEQUENCE is tag(CONT,PRIM,0) */
+#define SEQ_TAG_KEYID (ASN1_CONT << 6)
+
 /*
  * Process certificate extensions that are used to qualify the certificate.
  */
@@ -407,21 +410,57 @@ int x509_process_extension(void *context, size_t hdrlen,
        }
 
        if (ctx->last_oid == OID_authorityKeyIdentifier) {
+               size_t key_len;
+
                /* Get hold of the CA key fingerprint */
                if (vlen < 5)
                        return -EBADMSG;
-               if (v[0] != (ASN1_SEQ | (ASN1_CONS << 5)) ||
-                   v[1] != vlen - 2 ||
-                   v[2] != (ASN1_CONT << 6) ||
-                   v[3] != vlen - 4)
+
+               /* Authority Key Identifier must be a Constructed SEQUENCE */
+               if (v[0] != (ASN1_SEQ | (ASN1_CONS << 5)))
                        return -EBADMSG;
-               v += 4;
-               vlen -= 4;
 
-               f = kmalloc(vlen * 2 + 1, GFP_KERNEL);
+               /* Authority Key Identifier is not indefinite length */
+               if (unlikely(vlen == ASN1_INDEFINITE_LENGTH))
+                       return -EBADMSG;
+
+               if (vlen < ASN1_INDEFINITE_LENGTH) {
+                       /* Short Form length */
+                       if (v[1] != vlen - 2 ||
+                           v[2] != SEQ_TAG_KEYID ||
+                           v[3] > vlen - 4)
+                               return -EBADMSG;
+
+                       key_len = v[3];
+                       v += 4;
+               } else {
+                       /* Long Form length */
+                       size_t seq_len = 0;
+                       size_t sub = v[1] - ASN1_INDEFINITE_LENGTH;
+
+                       if (sub > 2)
+                               return -EBADMSG;
+
+                       /* calculate the length from subsequent octets */
+                       v += 2;
+                       for (i = 0; i < sub; i++) {
+                               seq_len <<= 8;
+                               seq_len |= v[i];
+                       }
+
+                       if (seq_len != vlen - 2 - sub ||
+                           v[sub] != SEQ_TAG_KEYID ||
+                           v[sub + 1] > vlen - 4 - sub)
+                               return -EBADMSG;
+
+                       key_len = v[sub + 1];
+                       v += (sub + 2);
+               }
+
+               f = kmalloc(key_len * 2 + 1, GFP_KERNEL);
                if (!f)
                        return -ENOMEM;
-               for (i = 0; i < vlen; i++)
+               for (i = 0; i < key_len; i++)
                        sprintf(f + i * 2, "%02x", v[i]);
                pr_debug("authority   %s\n", f);
                ctx->cert->authority = f;