Land rapid7#9029, Fix Linux post module file assumptions

Author: acammack-r7

modules/post/linux/gather/mount_cifs_creds.rb

@@ -38,6 +38,7 @@ def run
     ])
 
     # parse each line from /etc/fstab
+    fail_with(Failure::NotFound, '/etc/fstab not found on system') unless file_exist?('/etc/fstab')
     read_file("/etc/fstab").each_line do |fstab_line|
       fstab_line.strip!
       # where we'll store the current parsed credentials, if any

modules/post/multi/escalate/metasploit_pcaplog.rb

@@ -61,6 +61,7 @@ def normalize_minutes
 
   def run
     print_status "Setting up the victim's /tmp dir"
+    fail_with(Failure::NotFound, '/etc/passwd not found on system') unless file_exist?('/etc/passwd')
     initial_size = read_file("/etc/passwd").lines.count
     print_status "/etc/passwd is currently #{initial_size} lines long"
     i = 0

modules/post/multi/gather/enum_vbox.rb

@@ -55,6 +55,7 @@ def run
       end
     end
 
+    return nil unless res
     vprint_status(res)
     store_path = store_loot('virtualbox_vms', "text/plain", session, res, "virtualbox_vms.txt", "Virtualbox Virtual Machines")
     print_good("#{peer} - File successfully retrieved and saved on #{store_path}")

modules/post/multi/gather/lastpass_creds.rb

@@ -194,7 +194,7 @@ def user_profiles
     when /windows/
       user_profiles |= grab_user_profiles
     else
-      print_error "OS not recognized: #{os}"
+      print_error "OS not recognized: #{session.platform}"
     end
     user_profiles
   end

modules/post/multi/gather/remmina_creds.rb

@@ -67,7 +67,7 @@ def extract_all_creds
     user_dirs = enum_user_directories
     if user_dirs.empty?
       print_error('No user directories found')
-      return
+      return creds
     end
 
     vprint_status("Searching for Remmina creds in #{user_dirs.size} user directories")