Pass flags from agent sign request to ssh_key_sign.

Now each public-key algorithm gets to indicate what flags it supports,
and the ones it specifies support for may turn up in a call to its
sign() method.

We still don't actually support any flags yet, though.

pageant.c

@@ -323,7 +323,7 @@ void pageant_handle_msg(BinarySink *bs,
 	    struct ssh2_userkey *key;
             ptrlen keyblob, sigdata;
             strbuf *signature;
-            uint32_t flags;
+            uint32_t flags, supported_flags;
 
             plog(logctx, logfn, "request: SSH2_AGENTC_SIGN_REQUEST");
 
@@ -366,20 +366,22 @@ void pageant_handle_msg(BinarySink *bs,
             else
                 plog(logctx, logfn, "no signature flags");
 
-            if (flags) {
+            supported_flags = ssh_key_alg(key->key)->supported_flags;
+            if (flags & ~supported_flags) {
                 /*
                  * We MUST reject any message containing flags we
                  * don't understand.
                  */
                 char *msg = dupprintf(
-                    "unsupported flag bits 0x%08"PRIx32, flags);
+                    "unsupported flag bits 0x%08"PRIx32,
+                    flags & ~supported_flags);
                 pageant_failure_msg(bs, msg, logctx, logfn);
                 sfree(msg);
                 return;
             }
 
             signature = strbuf_new();
-            ssh_key_sign(key->key, sigdata.ptr, sigdata.len,
+            ssh_key_sign(key->key, sigdata.ptr, sigdata.len, flags,
                          BinarySink_UPCAST(signature));
 
             put_byte(bs, SSH2_AGENT_SIGN_RESPONSE);

ssh.h

@@ -770,7 +770,8 @@ struct ssh_keyalg {
 
     /* Methods that operate on an existing ssh_key */
     void (*freekey) (ssh_key *key);
-    void (*sign) (ssh_key *key, const void *data, int datalen, BinarySink *);
+    void (*sign) (ssh_key *key, const void *data, int datalen,
+                  unsigned flags, BinarySink *);
     bool (*verify) (ssh_key *key, ptrlen sig, ptrlen data);
     void (*public_blob)(ssh_key *key, BinarySink *);
     void (*private_blob)(ssh_key *key, BinarySink *);
@@ -784,6 +785,7 @@ struct ssh_keyalg {
     const char *ssh_id;    /* string identifier in the SSH protocol */
     const char *cache_id;  /* identifier used in PuTTY's host key cache */
     const void *extra;     /* private to the public key methods */
+    const unsigned supported_flags;    /* signature-type flags we understand */
 };
 
 #define ssh_key_new_pub(alg, data) ((alg)->new_pub(alg, data))
@@ -791,7 +793,8 @@ struct ssh_keyalg {
 #define ssh_key_new_priv_openssh(alg, bs) ((alg)->new_priv_openssh(alg, bs))
 
 #define ssh_key_free(key) ((*(key))->freekey(key))
-#define ssh_key_sign(key, data, len, bs) ((*(key))->sign(key, data, len, bs))
+#define ssh_key_sign(key, data, len, flags, bs) \
+    ((*(key))->sign(key, data, len, flags, bs))
 #define ssh_key_verify(key, sig, data) ((*(key))->verify(key, sig, data))
 #define ssh_key_public_blob(key, bs) ((*(key))->public_blob(key, bs))
 #define ssh_key_private_blob(key, bs) ((*(key))->private_blob(key, bs))

ssh2kex-server.c

@@ -27,7 +27,7 @@ static strbuf *finalise_and_sign_exhash(struct ssh2_transport_state *s)
     strbuf *sb;
     ssh2transport_finalise_exhash(s);
     sb = strbuf_new();
-    ssh_key_sign(s->hkey, s->exchange_hash, s->kex_alg->hash->hlen,
+    ssh_key_sign(s->hkey, s->exchange_hash, s->kex_alg->hash->hlen, 0,
                  BinarySink_UPCAST(sb));
     return sb;
 }

ssh2userauth.c

@@ -863,7 +863,7 @@ static void ssh2_userauth_process_queue(PacketProtocolLayer *ppl)
                     put_data(sigdata, s->pktout->data + 5,
                              s->pktout->length - 5);
                     sigblob = strbuf_new();
-                    ssh_key_sign(key->key, sigdata->s, sigdata->len,
+                    ssh_key_sign(key->key, sigdata->s, sigdata->len, 0,
                                  BinarySink_UPCAST(sigblob));
                     strbuf_free(sigdata);
                     ssh2_userauth_add_sigblob(

sshdss.c

@@ -447,7 +447,7 @@ Bignum *dss_gen_k(const char *id_string, Bignum modulus, Bignum private_key,
 }
 
 static void dss_sign(ssh_key *key, const void *data, int datalen,
-                     BinarySink *bs)
+                     unsigned flags, BinarySink *bs)
 {
     struct dss_key *dss = container_of(key, struct dss_key, sshk);
     Bignum k, gkp, hash, kinv, hxr, r, s;
@@ -504,4 +504,5 @@ const ssh_keyalg ssh_dss = {
     "ssh-dss",
     "dss",
     NULL,
+    0, /* no supported flags */
 };

sshecc.c

@@ -2257,7 +2257,7 @@ static bool ecdsa_verify(ssh_key *key, ptrlen sig, ptrlen data)
 }
 
 static void ecdsa_sign(ssh_key *key, const void *data, int datalen,
-                       BinarySink *bs)
+                       unsigned flags, BinarySink *bs)
 {
     struct ec_key *ec = container_of(key, struct ec_key, sshk);
     const struct ecsign_extra *extra =
@@ -2413,6 +2413,7 @@ const ssh_keyalg ssh_ecdsa_ed25519 = {
     "ssh-ed25519",
     "ssh-ed25519",
     &sign_extra_ed25519,
+    0, /* no supported flags */
 };
 
 /* OID: 1.2.840.10045.3.1.7 (ansiX9p256r1) */
@@ -2441,6 +2442,7 @@ const ssh_keyalg ssh_ecdsa_nistp256 = {
     "ecdsa-sha2-nistp256",
     "ecdsa-sha2-nistp256",
     &sign_extra_nistp256,
+    0, /* no supported flags */
 };
 
 /* OID: 1.3.132.0.34 (secp384r1) */
@@ -2469,6 +2471,7 @@ const ssh_keyalg ssh_ecdsa_nistp384 = {
     "ecdsa-sha2-nistp384",
     "ecdsa-sha2-nistp384",
     &sign_extra_nistp384,
+    0, /* no supported flags */
 };
 
 /* OID: 1.3.132.0.35 (secp521r1) */
@@ -2497,6 +2500,7 @@ const ssh_keyalg ssh_ecdsa_nistp521 = {
     "ecdsa-sha2-nistp521",
     "ecdsa-sha2-nistp521",
     &sign_extra_nistp521,
+    0, /* no supported flags */
 };
 
 /* ----------------------------------------------------------------------

sshrsa.c

@@ -744,7 +744,7 @@ static bool rsa2_verify(ssh_key *key, ptrlen sig, ptrlen data)
 }
 
 static void rsa2_sign(ssh_key *key, const void *data, int datalen,
-                      BinarySink *bs)
+                      unsigned flags, BinarySink *bs)
 {
     struct RSAKey *rsa = container_of(key, struct RSAKey, sshk);
     unsigned char *bytes;
@@ -800,6 +800,7 @@ const ssh_keyalg ssh_rsa = {
     "ssh-rsa",
     "rsa2",
     NULL,
+    0, /* no supported flags */
 };
 
 struct RSAKey *ssh_rsakex_newkey(const void *data, int len)