Replace manual ASN1 decoder with ASN1_get_object

Replace manual ASN.1 decoder with ASN1_get object. This
will decode the tag and length properly and check against
it does not exceed the supplied buffer length.

PR#3335
(cherry picked from commit b0308dddd1cc6a8e1de803ef29ba6da25ee072c2)

diff --git a/ssl/s3_srvr.c b/ssl/s3_srvr.c
index 9ac19c05f22d201a27b1e6fe63d8319d6dd81228..4de9d1900f5dde61719af41674379ebcf0a2f042 100644 (file)
--- a/ssl/s3_srvr.c
+++ b/ssl/s3_srvr.c
@@ -2813,6 +2813,8 @@ int ssl3_get_client_key_exchange(SSL *s)
                        unsigned char premaster_secret[32], *start;
                        size_t outlen=32, inlen;
                        unsigned long alg_a;
+                       int Ttag, Tclass;
+                       long Tlen;
 
                        /* Get our certificate private key*/
                        alg_a = s->s3->tmp.new_cipher->algorithm_auth;
@@ -2834,26 +2836,15 @@ int ssl3_get_client_key_exchange(SSL *s)
                                        ERR_clear_error();
                                }
                        /* Decrypt session key */
-                       if ((*p!=( V_ASN1_SEQUENCE| V_ASN1_CONSTRUCTED))) 
-                               {
-                               SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_DECRYPTION_FAILED);
-                               goto gerr;
-                               }
-                       if (p[1] == 0x81)
-                               {
-                               start = p+3;
-                               inlen = p[2];
-                               }
-                       else if (p[1] < 0x80)
-                               {
-                               start = p+2;
-                               inlen = p[1];
-                               }
-                       else
+                       if (ASN1_get_object((const unsigned char **)&p, &Tlen, &Ttag, &Tclass, n) != V_ASN1_CONSTRUCTED || 
+                               Ttag != V_ASN1_SEQUENCE ||
+                               Tclass != V_ASN1_UNIVERSAL) 
                                {
                                SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_DECRYPTION_FAILED);
                                goto gerr;
                                }
+                       start = p;
+                       inlen = Tlen;
                        if (EVP_PKEY_decrypt(pkey_ctx,premaster_secret,&outlen,start,inlen) <=0) 
 
                                {