sftp: Allocate a new buffer in sftp_packet_read() if needed

We will move the buffer to the message instead of duplicating the
memory.

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>

src/sftp.c

@@ -339,11 +339,23 @@ sftp_packet sftp_packet_read(sftp_session sftp)
 
     packet->sftp = sftp;
 
+    /*
+     * If the packet has a payload, then just reinit the buffer, otherwise
+     * allocate a new one.
+     */
+    if (packet->payload != NULL) {
         rc = ssh_buffer_reinit(packet->payload);
         if (rc != 0) {
             ssh_set_error_oom(sftp->session);
             return NULL;
         }
+    } else {
+        packet->payload = ssh_buffer_new();
+        if (packet->payload == NULL) {
+            ssh_set_error_oom(sftp->session);
+            return NULL;
+        }
+    }
 
     nread = 0;
     do {