crypto: push error reporting into TLS session I/O APIs

The current TLS session I/O APIs just return a synthetic errno
value on error, which has been translated from a gnutls error
value. This looses a large amount of valuable information that
distinguishes different scenarios.

Pushing population of the "Error *errp" object into the TLS
session I/O APIs gives more detailed error information.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

3 files changed, 68 insertions, 63 deletions

diff --git a/crypto/tlssession.c b/crypto/tlssession.c
index 1e98f44e0d..926f19c115 100644
--- a/crypto/tlssession.c
+++ b/crypto/tlssession.c
@@ -441,23 +441,20 @@ qcrypto_tls_session_set_callbacks(QCryptoTLSSession *session,
 ssize_t
 qcrypto_tls_session_write(QCryptoTLSSession *session,
                           const char *buf,
-                          size_t len)
+                          size_t len,
+                          Error **errp)
 {
     ssize_t ret = gnutls_record_send(session->handle, buf, len);
 
     if (ret < 0) {
-        switch (ret) {
-        case GNUTLS_E_AGAIN:
-            errno = EAGAIN;
-            break;
-        case GNUTLS_E_INTERRUPTED:
-            errno = EINTR;
-            break;
-        default:
-            errno = EIO;
-            break;
+        if (ret == GNUTLS_E_AGAIN) {
+            return QCRYPTO_TLS_SESSION_ERR_BLOCK;
+        } else {
+            error_setg(errp,
+                       "Cannot write to TLS channel: %s",
+                       gnutls_strerror(ret));
+            return -1;
         }
-        ret = -1;
     }
 
     return ret;
@@ -467,26 +464,24 @@ qcrypto_tls_session_write(QCryptoTLSSession *session,
 ssize_t
 qcrypto_tls_session_read(QCryptoTLSSession *session,
                          char *buf,
-                         size_t len)
+                         size_t len,
+                         bool gracefulTermination,
+                         Error **errp)
 {
     ssize_t ret = gnutls_record_recv(session->handle, buf, len);
 
     if (ret < 0) {
-        switch (ret) {
-        case GNUTLS_E_AGAIN:
-            errno = EAGAIN;
-            break;
-        case GNUTLS_E_INTERRUPTED:
-            errno = EINTR;
-            break;
-        case GNUTLS_E_PREMATURE_TERMINATION:
-            errno = ECONNABORTED;
-            break;
-        default:
-            errno = EIO;
-            break;
+        if (ret == GNUTLS_E_AGAIN) {
+            return QCRYPTO_TLS_SESSION_ERR_BLOCK;
+        } else if ((ret == GNUTLS_E_PREMATURE_TERMINATION) &&
+                   gracefulTermination){
+            return 0;
+        } else {
+            error_setg(errp,
+                       "Cannot read from TLS channel: %s",
+                       gnutls_strerror(ret));
+            return -1;
         }
-        ret = -1;
     }
 
     return ret;
@@ -605,9 +600,10 @@ qcrypto_tls_session_set_callbacks(
 ssize_t
 qcrypto_tls_session_write(QCryptoTLSSession *sess,
                           const char *buf,
-                          size_t len)
+                          size_t len,
+                          Error **errp)
 {
-    errno = -EIO;
+    error_setg(errp, "TLS requires GNUTLS support");
     return -1;
 }
 
@@ -615,9 +611,11 @@ qcrypto_tls_session_write(QCryptoTLSSession *sess,
 ssize_t
 qcrypto_tls_session_read(QCryptoTLSSession *sess,
                          char *buf,
-                         size_t len)
+                         size_t len,
+                         bool gracefulTermination,
+                         Error **errp)
 {
-    errno = -EIO;
+    error_setg(errp, "TLS requires GNUTLS support");
     return -1;
 }
 
diff --git a/include/crypto/tlssession.h b/include/crypto/tlssession.h
index 571049bd0e..291e602540 100644
--- a/include/crypto/tlssession.h
+++ b/include/crypto/tlssession.h
@@ -107,6 +107,7 @@
 
 typedef struct QCryptoTLSSession QCryptoTLSSession;
 
+#define QCRYPTO_TLS_SESSION_ERR_BLOCK -2
 
 /**
  * qcrypto_tls_session_new:
@@ -212,6 +213,7 @@ void qcrypto_tls_session_set_callbacks(QCryptoTLSSession *sess,
  * @sess: the TLS session object
  * @buf: the plain text to send
  * @len: the length of @buf
+ * @errp: pointer to hold returned error object
  *
  * Encrypt @len bytes of the data in @buf and send
  * it to the remote peer using the callback previously
@@ -221,32 +223,45 @@ void qcrypto_tls_session_set_callbacks(QCryptoTLSSession *sess,
  * qcrypto_tls_session_get_handshake_status() returns
  * QCRYPTO_TLS_HANDSHAKE_COMPLETE
  *
- * Returns: the number of bytes sent, or -1 on error
+ * Returns: the number of bytes sent,
+ * or QCRYPTO_TLS_SESSION_ERR_BLOCK if the write would block,
+ * or -1 on error.
  */
 ssize_t qcrypto_tls_session_write(QCryptoTLSSession *sess,
                                   const char *buf,
-                                  size_t len);
+                                  size_t len,
+                                  Error **errp);
 
 /**
  * qcrypto_tls_session_read:
  * @sess: the TLS session object
  * @buf: to fill with plain text received
  * @len: the length of @buf
+ * @gracefulTermination: treat premature termination as graceful EOF
+ * @errp: pointer to hold returned error object
  *
  * Receive up to @len bytes of data from the remote peer
  * using the callback previously registered with
  * qcrypto_tls_session_set_callbacks(), decrypt it and
  * store it in @buf.
  *
+ * If @gracefulTermination is true, then a premature termination
+ * of the TLS session will be treated as indicating EOF, as
+ * opposed to an error.
+ *
  * It is an error to call this before
  * qcrypto_tls_session_get_handshake_status() returns
  * QCRYPTO_TLS_HANDSHAKE_COMPLETE
  *
- * Returns: the number of bytes received, or -1 on error
+ * Returns: the number of bytes received,
+ * or QCRYPTO_TLS_SESSION_ERR_BLOCK if the receive would block,
+ * or -1 on error.
  */
 ssize_t qcrypto_tls_session_read(QCryptoTLSSession *sess,
                                  char *buf,
-                                 size_t len);
+                                 size_t len,
+                                 bool gracefulTermination,
+                                 Error **errp);
 
 /**
  * qcrypto_tls_session_check_pending:
diff --git a/io/channel-tls.c b/io/channel-tls.c
index 67b9700006..9d8bb158d1 100644
--- a/io/channel-tls.c
+++ b/io/channel-tls.c
@@ -277,24 +277,19 @@ static ssize_t qio_channel_tls_readv(QIOChannel *ioc,
     ssize_t got = 0;
 
     for (i = 0 ; i < niov ; i++) {
-        ssize_t ret = qcrypto_tls_session_read(tioc->session,
-                                               iov[i].iov_base,
-                                               iov[i].iov_len);
-        if (ret < 0) {
-            if (errno == EAGAIN) {
-                if (got) {
-                    return got;
-                } else {
-                    return QIO_CHANNEL_ERR_BLOCK;
-                }
-            } else if (errno == ECONNABORTED &&
-                       (qatomic_load_acquire(&tioc->shutdown) &
-                        QIO_CHANNEL_SHUTDOWN_READ)) {
-                return 0;
+        ssize_t ret = qcrypto_tls_session_read(
+            tioc->session,
+            iov[i].iov_base,
+            iov[i].iov_len,
+            qatomic_load_acquire(&tioc->shutdown) & QIO_CHANNEL_SHUTDOWN_READ,
+            errp);
+        if (ret == QCRYPTO_TLS_SESSION_ERR_BLOCK) {
+            if (got) {
+                return got;
+            } else {
+                return QIO_CHANNEL_ERR_BLOCK;
             }
-
-            error_setg_errno(errp, errno,
-                             "Cannot read from TLS channel");
+        } else if (ret < 0) {
             return -1;
         }
         got += ret;
@@ -321,18 +316,15 @@ static ssize_t qio_channel_tls_writev(QIOChannel *ioc,
     for (i = 0 ; i < niov ; i++) {
         ssize_t ret = qcrypto_tls_session_write(tioc->session,
                                                 iov[i].iov_base,
-                                                iov[i].iov_len);
-        if (ret <= 0) {
-            if (errno == EAGAIN) {
-                if (done) {
-                    return done;
-                } else {
-                    return QIO_CHANNEL_ERR_BLOCK;
-                }
+                                                iov[i].iov_len,
+                                                errp);
+        if (ret == QCRYPTO_TLS_SESSION_ERR_BLOCK) {
+            if (done) {
+                return done;
+            } else {
+                return QIO_CHANNEL_ERR_BLOCK;
             }
-
-            error_setg_errno(errp, errno,
-                             "Cannot write to TLS channel");
+        } else if (ret < 0) {
             return -1;
         }
         done += ret;