upstream: translate and return error codes; retry on bad PIN

Define some well-known error codes in the SK API and pass
them back via ssh-sk-helper.

Use the new "wrong PIN" error code to retry PIN prompting during
ssh-keygen of resident keys.

feedback and ok markus@

OpenBSD-Commit-ID: 9663c6a2bb7a0bc8deaccc6c30d9a2983b481620

6 files changed, 82 insertions, 34 deletions

diff --git a/sk-api.h b/sk-api.h
index 4f9f43ee6..dc786d556 100644
--- a/sk-api.h
+++ b/sk-api.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: sk-api.h,v 1.5 2019/12/30 09:23:28 djm Exp $ */
+/* $OpenBSD: sk-api.h,v 1.6 2019/12/30 09:24:45 djm Exp $ */
 /*
  * Copyright (c) 2019 Google LLC
  *
@@ -32,6 +32,11 @@
 #define SSH_SK_ECDSA                    0x00
 #define SSH_SK_ED25519                  0x01
 
+/* Error codes */
+#define SSH_SK_ERR_GENERAL              -1
+#define SSH_SK_ERR_UNSUPPORTED          -2
+#define SSH_SK_ERR_PIN_REQUIRED         -3
+
 struct sk_enroll_response {
         uint8_t *public_key;
         size_t public_key_len;
diff --git a/sk-usbhid.c b/sk-usbhid.c
index 54ce0bddf..22a4c5df5 100644
--- a/sk-usbhid.c
+++ b/sk-usbhid.c
@@ -65,6 +65,11 @@
 #define SK_ECDSA                0x00
 #define SK_ED25519              0x01
 
+/* Error codes */
+#define SSH_SK_ERR_GENERAL              -1
+#define SSH_SK_ERR_UNSUPPORTED          -2
+#define SSH_SK_ERR_PIN_REQUIRED         -3
+
 struct sk_enroll_response {
         uint8_t *public_key;
         size_t public_key_len;
@@ -412,6 +417,20 @@ pack_public_key(int alg, const fido_cred_t *cred,
         }
 }
 
+static int
+fidoerr_to_skerr(int fidoerr)
+{
+        switch (fidoerr) {
+        case FIDO_ERR_UNSUPPORTED_OPTION:
+                return SSH_SK_ERR_UNSUPPORTED;
+        case FIDO_ERR_PIN_REQUIRED:
+        case FIDO_ERR_PIN_INVALID:
+                return SSH_SK_ERR_PIN_REQUIRED;
+        default:
+                return -1;
+        }
+}
+
 int
 sk_enroll(int alg, const uint8_t *challenge, size_t challenge_len,
     const char *application, uint8_t flags, const char *pin,
@@ -424,7 +443,7 @@ sk_enroll(int alg, const uint8_t *challenge, size_t challenge_len,
         struct sk_enroll_response *response = NULL;
         size_t len;
         int cose_alg;
-        int ret = -1;
+        int ret = SSH_SK_ERR_GENERAL;
         int r;
         char *device = NULL;
 
@@ -491,8 +510,9 @@ sk_enroll(int alg, const uint8_t *challenge, size_t challenge_len,
                 skdebug(__func__, "fido_dev_open: %s", fido_strerr(r));
                 goto out;
         }
-        if ((r = fido_dev_make_cred(dev, cred, NULL)) != FIDO_OK) {
+        if ((r = fido_dev_make_cred(dev, cred, pin)) != FIDO_OK) {
                 skdebug(__func__, "fido_dev_make_cred: %s", fido_strerr(r));
+                ret = fidoerr_to_skerr(r);
                 goto out;
         }
         if (fido_cred_x5c_ptr(cred) != NULL) {
@@ -657,7 +677,7 @@ sk_sign(int alg, const uint8_t *message, size_t message_len,
         fido_assert_t *assert = NULL;
         fido_dev_t *dev = NULL;
         struct sk_sign_response *response = NULL;
-        int ret = -1;
+        int ret = SSH_SK_ERR_GENERAL;
         int r;
 
 #ifdef SK_DEBUG
@@ -736,7 +756,7 @@ static int
 read_rks(const char *devpath, const char *pin,
     struct sk_resident_key ***rksp, size_t *nrksp)
 {
-        int r = -1;
+        int ret = SSH_SK_ERR_GENERAL, r = -1;
         fido_dev_t *dev = NULL;
         fido_credman_metadata_t *metadata = NULL;
         fido_credman_rp_t *rp = NULL;
@@ -747,16 +767,15 @@ read_rks(const char *devpath, const char *pin,
 
         if ((dev = fido_dev_new()) == NULL) {
                 skdebug(__func__, "fido_dev_new failed");
-                return -1;
+                return ret;
         }
         if ((r = fido_dev_open(dev, devpath)) != FIDO_OK) {
                 skdebug(__func__, "fido_dev_open %s failed: %s",
                     devpath, fido_strerr(r));
                 fido_dev_free(&dev);
-                return -1;
+                return ret;
         }
         if ((metadata = fido_credman_metadata_new()) == NULL) {
-                r = -1;
                 skdebug(__func__, "alloc failed");
                 goto out;
         }
@@ -765,7 +784,7 @@ read_rks(const char *devpath, const char *pin,
                 if (r == FIDO_ERR_INVALID_COMMAND) {
                         skdebug(__func__, "device %s does not support "
                             "resident keys", devpath);
-                        r = 0;
+                        ret = 0;
                         goto out;
                 }
                 skdebug(__func__, "get metadata for %s failed: %s",
@@ -776,7 +795,6 @@ read_rks(const char *devpath, const char *pin,
             (unsigned long long)fido_credman_rk_existing(metadata),
             (unsigned long long)fido_credman_rk_remaining(metadata));
         if ((rp = fido_credman_rp_new()) == NULL) {
-                r = -1;
                 skdebug(__func__, "alloc rp failed");
                 goto out;
         }
@@ -801,7 +819,6 @@ read_rks(const char *devpath, const char *pin,
 
                 fido_credman_rk_free(&rk);
                 if ((rk = fido_credman_rk_new()) == NULL) {
-                        r = -1;
                         skdebug(__func__, "alloc rk failed");
                         goto out;
                 }
@@ -831,7 +848,6 @@ read_rks(const char *devpath, const char *pin,
                             fido_cred_id_len(cred))) == NULL ||
                             (srk->application = strdup(fido_credman_rp_id(rp,
                             i))) == NULL) {
-                                r = -1;
                                 skdebug(__func__, "alloc sk_resident_key");
                                 goto out;
                         }
@@ -862,7 +878,6 @@ read_rks(const char *devpath, const char *pin,
                         /* append */
                         if ((tmp = recallocarray(*rksp, *nrksp, (*nrksp) + 1,
                             sizeof(**rksp))) == NULL) {
-                                r = -1;
                                 skdebug(__func__, "alloc rksp");
                                 goto out;
                         }
@@ -872,7 +887,7 @@ read_rks(const char *devpath, const char *pin,
                 }
         }
         /* Success */
-        r = 0;
+        ret = 0;
  out:
         if (srk != NULL) {
                 free(srk->application);
@@ -885,14 +900,14 @@ read_rks(const char *devpath, const char *pin,
         fido_dev_close(dev);
         fido_dev_free(&dev);
         fido_credman_metadata_free(&metadata);
-        return r;
+        return ret;
 }
 
 int
 sk_load_resident_keys(const char *pin,
     struct sk_resident_key ***rksp, size_t *nrksp)
 {
-        int r = -1;
+        int ret = SSH_SK_ERR_GENERAL, r = -1;
         fido_dev_info_t *devlist = NULL;
         size_t i, ndev = 0, nrks = 0;
         const fido_dev_info_t *di;
@@ -924,7 +939,7 @@ sk_load_resident_keys(const char *pin,
                 }
         }
         /* success */
-        r = 0;
+        ret = 0;
         *rksp = rks;
         *nrksp = nrks;
         rks = NULL;
@@ -938,7 +953,7 @@ sk_load_resident_keys(const char *pin,
         }
         free(rks);
         fido_dev_info_free(&devlist, MAX_FIDO_DEVICES);
-        return r;
+        return ret;
 }
 
 #endif /* ENABLE_SK_INTERNAL */
diff --git a/ssh-keygen.c b/ssh-keygen.c
index 79e2e92b5..696891e0e 100644
--- a/ssh-keygen.c
+++ b/ssh-keygen.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-keygen.c,v 1.378 2019/12/30 09:23:28 djm Exp $ */
+/* $OpenBSD: ssh-keygen.c,v 1.379 2019/12/30 09:24:45 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1994 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -3361,16 +3361,26 @@ main(int argc, char **argv)
         switch (type) {
         case KEY_ECDSA_SK:
         case KEY_ED25519_SK:
-                if (!quiet) {
-                        printf("You may need to touch your security key "
-                            "to authorize key generation.\n");
-                }
-                fflush(stdout);
-                if (sshsk_enroll(type, sk_provider,
-                    cert_key_id == NULL ? "ssh:" : cert_key_id,
-                    sk_flags, NULL, NULL, &private, NULL) != 0)
-                        exit(1); /* error message already printed */
-                break;
+                passphrase1 = NULL;
+                for (i = 0 ; i < 3; i++) {
+                        if (!quiet) {
+                                printf("You may need to touch your security "
+                                    "key to authorize key generation.\n");
+                        }
+                        fflush(stdout);
+                        r = sshsk_enroll(type, sk_provider,
+                            cert_key_id == NULL ? "ssh:" : cert_key_id,
+                            sk_flags, passphrase1, NULL, &private, NULL);
+                        if (r == 0)
+                                break;
+                        if (r != SSH_ERR_KEY_WRONG_PASSPHRASE)
+                                exit(1); /* error message already printed */
+                        passphrase1 = read_passphrase("Enter PIN for security "
+                            "key: ", RP_ALLOW_STDIN);
+                }
+                if (i > 3)
+                        fatal("Too many incorrect PINs");
+                break;
         default:
                 if ((r = sshkey_generate(type, bits, &private)) != 0)
                         fatal("sshkey_generate failed");
diff --git a/ssh-sk.c b/ssh-sk.c
index e1fb72cfc..b1d0d6c58 100644
--- a/ssh-sk.c
+++ b/ssh-sk.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-sk.c,v 1.22 2019/12/30 09:24:03 djm Exp $ */
+/* $OpenBSD: ssh-sk.c,v 1.23 2019/12/30 09:24:45 djm Exp $ */
 /*
  * Copyright (c) 2019 Google LLC
  *
@@ -325,6 +325,20 @@ sshsk_key_from_response(int alg, const char *application, uint8_t flags,
         return r;
 }
 
+static int
+skerr_to_ssherr(int skerr)
+{
+        switch (skerr) {
+        case SSH_SK_ERR_UNSUPPORTED:
+                return SSH_ERR_FEATURE_UNSUPPORTED;
+        case SSH_SK_ERR_PIN_REQUIRED:
+                return SSH_ERR_KEY_WRONG_PASSPHRASE;
+        case SSH_SK_ERR_GENERAL:
+        default:
+                return SSH_ERR_INVALID_FORMAT;
+        }
+}
+
 int
 sshsk_enroll(int type, const char *provider_path, const char *application,
     uint8_t flags, const char *pin, struct sshbuf *challenge_buf,
@@ -396,7 +410,7 @@ sshsk_enroll(int type, const char *provider_path, const char *application,
             flags, pin, &resp)) != 0) {
                 error("Security key provider \"%s\" returned failure %d",
                     provider_path, r);
-                r = SSH_ERR_INVALID_FORMAT; /* XXX error codes in API? */
+                r = skerr_to_ssherr(r);
                 goto out;
         }
 
@@ -559,6 +573,7 @@ sshsk_sign(const char *provider_path, struct sshkey *key,
             sshbuf_ptr(key->sk_key_handle), sshbuf_len(key->sk_key_handle),
             key->sk_flags, pin, &resp)) != 0) {
                 debug("%s: sk_sign failed with code %d", __func__, r);
+                r = skerr_to_ssherr(r);
                 goto out;
         }
         /* Assemble signature */
@@ -655,7 +670,7 @@ sshsk_load_resident(const char *provider_path, const char *pin,
         if ((r = skp->sk_load_resident_keys(pin, &rks, &nrks)) != 0) {
                 error("Security key provider \"%s\" returned failure %d",
                     provider_path, r);
-                r = SSH_ERR_INVALID_FORMAT; /* XXX error codes in API? */
+                r = skerr_to_ssherr(r);
                 goto out;
         }
         for (i = 0; i < nrks; i++) {
diff --git a/ssherr.c b/ssherr.c
index 8ad3d5750..38974f51b 100644
--- a/ssherr.c
+++ b/ssherr.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: ssherr.c,v 1.8 2018/07/03 11:39:54 djm Exp $  */
+/*      $OpenBSD: ssherr.c,v 1.9 2019/12/30 09:24:45 djm Exp $  */
 /*
  * Copyright (c) 2011 Damien Miller
  *
@@ -141,6 +141,8 @@ ssh_err(int n)
                 return "number is too large";
         case SSH_ERR_SIGN_ALG_UNSUPPORTED:
                 return "signature algorithm not supported";
+        case SSH_ERR_FEATURE_UNSUPPORTED:
+                return "requested feature not supported";
         default:
                 return "unknown error";
         }
diff --git a/ssherr.h b/ssherr.h
index 348da5a20..520bd4964 100644
--- a/ssherr.h
+++ b/ssherr.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: ssherr.h,v 1.6 2018/07/03 11:39:54 djm Exp $  */
+/*      $OpenBSD: ssherr.h,v 1.7 2019/12/30 09:24:45 djm Exp $  */
 /*
  * Copyright (c) 2011 Damien Miller
  *
@@ -80,6 +80,7 @@
 #define SSH_ERR_KEY_LENGTH                      -56
 #define SSH_ERR_NUMBER_TOO_LARGE                -57
 #define SSH_ERR_SIGN_ALG_UNSUPPORTED            -58
+#define SSH_ERR_FEATURE_UNSUPPORTED             -59
 
 /* Translate a numeric error code to a human-readable error string */
 const char *ssh_err(int n);