Feature an optional crypto-specific macro to rsa sign a data fragment vector

OS/400 crypto library is unable to sign a precomputed SHA1 hash: however
it does support a procedure that hashes data fragments and rsa signs.
If defined, the new macro _libssh2_rsa_sha1_signv() implements this function
and disables use of _libssh2_rsa_sha1_sign().

The function described above requires that the struct iovec unused slacks are
cleared: for this reason, macro libssh2_prepare_iovec() has been introduced.
It should be defined as empty for crypto backends that are not sensitive
to struct iovec unused slack values.

src/hostkey.c

@@ -200,6 +200,11 @@ hostkey_method_ssh_rsa_signv(LIBSSH2_SESSION * session,
                              void **abstract)
 {
     libssh2_rsa_ctx *rsactx = (libssh2_rsa_ctx *) (*abstract);
+
+#ifdef _libssh2_rsa_sha1_signv
+    return _libssh2_rsa_sha1_signv(session, signature, signature_len,
+                                   veccount, datavec, rsactx);
+#else
     int ret;
     int i;
     unsigned char hash[SHA_DIGEST_LENGTH];
@@ -218,6 +223,7 @@ hostkey_method_ssh_rsa_signv(LIBSSH2_SESSION * session,
     }
 
     return 0;
+#endif
 }
 
 /*

src/libgcrypt.h

@@ -62,6 +62,8 @@
 #define _libssh2_random(buf, len)                \
   (gcry_randomize ((buf), (len), GCRY_STRONG_RANDOM), 1)
 
+#define libssh2_prepare_iovec(vec, len)  /* Empty. */
+
 #define libssh2_sha1_ctx gcry_md_hd_t
 
 /* returns 0 in case of failure */

src/openssl.h

@@ -114,6 +114,8 @@
 
 #define _libssh2_random(buf, len) RAND_bytes ((buf), (len))
 
+#define libssh2_prepare_iovec(vec, len)  /* Empty. */
+
 #if OPENSSL_VERSION_NUMBER >= 0x10100000L
 #define libssh2_sha1_ctx EVP_MD_CTX *
 #else

src/userauth.c

@@ -716,6 +716,7 @@ sign_frommemory(LIBSSH2_SESSION *session, unsigned char **sig, size_t *sig_len,
     if(rc)
         return rc;
 
+    libssh2_prepare_iovec(&datavec, 1);
     datavec.iov_base = (void *)data;
     datavec.iov_len  = data_len;
 
@@ -751,6 +752,7 @@ sign_fromfile(LIBSSH2_SESSION *session, unsigned char **sig, size_t *sig_len,
     if(rc)
         return rc;
 
+    libssh2_prepare_iovec(&datavec, 1);
     datavec.iov_base = (void *)data;
     datavec.iov_len  = data_len;
 
@@ -873,6 +875,7 @@ userauth_hostbased_fromfile(LIBSSH2_SESSION *session,
         }
 
         _libssh2_htonu32(buf, session->session_id_len);
+        libssh2_prepare_iovec(datavec, 4);
         datavec[0].iov_base = (void *)buf;
         datavec[0].iov_len = 4;
         datavec[1].iov_base = (void *)session->session_id;

src/wincng.h

@@ -111,6 +111,8 @@ void _libssh2_wincng_free(void);
 #define _libssh2_random(buf, len) \
   _libssh2_wincng_random(buf, len)
 
+#define libssh2_prepare_iovec(vec, len)  /* Empty. */
+
 
 /*******************************************************************/
 /*