Check for OpenSSH and implement sftp_symlink correct.

When OpenSSH's sftp-server was implemented, the order of the arguments
to the SSH_FXP_SYMLINK method was inadvertently reversed. Unfortunately,
the reversal was not noticed until the server was widely deployed.
Since fixing this to follow the specification would cause
incompatibility, the current order was retained.

include/libssh/libssh.h

@@ -217,6 +217,7 @@ int ssh_connect(SSH_SESSION *session);
 void ssh_disconnect(SSH_SESSION *session);
 int ssh_service_request(SSH_SESSION *session, const char *service);
 char *ssh_get_issue_banner(SSH_SESSION *session);
+int ssh_get_openssh_version(ssh_session session);
 /* get copyright informations */
 const char *ssh_copyright(void);
 

include/libssh/priv.h

@@ -340,6 +340,7 @@ struct ssh_session_struct {
     int protoversion;
     int server;
     int client;
+    int openssh;
     uint32_t send_seq;
     uint32_t recv_seq;
 /* status flags */

libssh/client.c

@@ -98,7 +98,10 @@ char *ssh_get_banner(SSH_SESSION *session) {
  * @see ssh_get_banner()
  */
 static int ssh_analyze_banner(SSH_SESSION *session, int *ssh1, int *ssh2) {
-  char *banner = session->serverbanner;
+  const char *banner = session->serverbanner;
+  const char *openssh;
+
+  ssh_log(session, SSH_LOG_RARE, "Analyzing banner: %s", banner);
 
   if (strncmp(banner, "SSH-", 4) != 0) {
     ssh_set_error(session, SSH_FATAL, "Protocol mismatch: %s", banner);
@@ -129,6 +132,17 @@ static int ssh_analyze_banner(SSH_SESSION *session, int *ssh1, int *ssh2) {
       return -1;
   }
 
+  openssh = strstr(banner, "OpenSSH");
+  if (openssh != NULL) {
+    int major, minor;
+    major = strtol(openssh + 8, (char **) NULL, 10);
+    minor = strtol(openssh + 10, (char **) NULL, 10);
+    session->openssh = SSH_VERSION_INT(major, minor, 0);
+    ssh_log(session, SSH_LOG_RARE,
+        "We are talking to an OpenSSH server version: %d.%d (%x)",
+        major, minor, session->openssh);
+  }
+
   return 0;
 }
 
@@ -615,6 +629,24 @@ char *ssh_get_issue_banner(SSH_SESSION *session) {
   return string_to_char(session->banner);
 }
 
+/**
+ * @brief Get the version of the OpenSSH server, if it is not an OpenSSH server
+ * then 0 will be returned.
+ *
+ * You can use the SSH_VERSION_INT macro to compare version numbers.
+ *
+ * @param  session      The SSH session to use.
+ *
+ * @return The version number if available, 0 otherwise.
+ */
+int ssh_get_openssh_version(ssh_session session) {
+  if (session == NULL) {
+    return 0;
+  }
+
+  return session->openssh;
+}
+
 /**
  * @brief Disconnect from a session (client or server).
  *

libssh/sftp.c

@@ -2247,10 +2247,32 @@ int sftp_symlink(SFTP_SESSION *sftp, const char *target, const char *dest) {
   }
 
   id = sftp_get_new_id(sftp);
-  if (buffer_add_u32(buffer, id) < 0 ||
-      buffer_add_ssh_string(buffer, target_s) < 0 ||
-      buffer_add_ssh_string(buffer, dest_s) < 0 ||
-      sftp_packet_write(sftp, SSH_FXP_SYMLINK, buffer) < 0) {
+  if (buffer_add_u32(buffer, id) < 0) {
+    buffer_free(buffer);
+    string_free(dest_s);
+    string_free(target_s);
+    return -1;
+  }
+  if (ssh_get_openssh_version(sftp->session)) {
+    /* TODO check for version number if they ever fix it. */
+    if (buffer_add_ssh_string(buffer, target_s) < 0 ||
+      buffer_add_ssh_string(buffer, dest_s) < 0) {
+      buffer_free(buffer);
+      string_free(dest_s);
+      string_free(target_s);
+      return -1;
+    }
+  } else {
+    if (buffer_add_ssh_string(buffer, dest_s) < 0 ||
+      buffer_add_ssh_string(buffer, target_s) < 0) {
+      buffer_free(buffer);
+      string_free(dest_s);
+      string_free(target_s);
+      return -1;
+    }
+  }
+
+  if (sftp_packet_write(sftp, SSH_FXP_SYMLINK, buffer) < 0) {
     buffer_free(buffer);
     string_free(dest_s);
     string_free(target_s);