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Accepted
Fabby
Asked: 2015-12-21 06:43:53 +0800 CST

How to enter password only once in a bash script needing sudo

  • 772

Data

  • I want operator users on this machine to mount their own cifs shares
  • The sudoers file already contains the /bin/mount -t cifs //*/* /media/* -o username=* command for all operators
  • I want the users to mount a cifs share through a script typing the password only once, not twice.
  • The sudo password and the cifs password are identical.

What I already have

This script works:

#!/bin/bash
sudo 'mount -t cifs //192.168.1.1/home /media/$USER/home -o username=$USER'

...but it requires the users to type the same password twice!

  • Once for sudo
  • Once for the mount itself

This would also work:

#!/bin/bash
echo -n Password: 
read -s szPassword
echo $szPassword | sudo -S sh -c 'echo $szPassword | mount -t cifs //192.168.1.1/home /media/$USER/home -o username=$USER'

...but this would require me to allow all operator users to be able to sudo sh (major security problem)

Question

How to mount a cifs share in bash¹ without putting sh in the sudoers file nor creating a permanent/temporary file???

Note 1: no python, perl, C, Go, ... please?
Note 2: I know I can just remove the password through the sudoers file, but I'm trying to tighten security, not loosen it, without giving up convenience...

bash

4 Answers

  1. You should instead make the user do the call of using sudo as sudo script. just check if the script is being run as root, if not ask for it

    if [[ $EUID -ne 0 ]]; then
   echo "This script must be run as root, use sudo "$0" instead" 1>&2
   exit 1
fi

    Don't try to capture the password of your users.

    • 27
  2. Best Answer

    I'm dumb!

    The following script:

    #!/bin/bash
read -p "Password: " -s szPassword
printf "%s\n" "$szPassword" | sudo --stdin mount -t cifs //192.168.1.1/home /media/$USER/home -o username=$USER,password="$szPassword"

    just works and:

    1. Doesn't create any files containing passwords
    2. Allows the user to type only one password for multiple shares (including Windows ones)
    3. Has no need for extra privileges to be granted. :-)
    • 10

  3. Require no sudo password for executing this command; the password prompt for mount remains.

    In sudoers, include something like

    ALL        ALL = NOPASSWD: /bin/mount -t cifs //*/* /media/* -o username=*

    After including this, sudo will no longer ask for a password for this specific command; the user still needs to provide a password to the mount command.

    Note: I took the command verbatim from what you included in the question; I didn't check whether its wildcards would allow for users to do something nasty. Read the sudoers manpage for examples of nastiness. In particular, note that this line in sudoers allows the user to add any number of -o switches or other arguments to mount. You may want to rethink your approach, e.g. by adding a script such as @Braiam proposes and allow running that through sudo without extra authentication. The script then ensures that users can only run the specific form of mount that you want them to run.

    Also, instead of allowing this for all users, you could also limit this to members of a certain group, e.g. you could create a group cifsmount and then have

    %cifsmount ALL = NOPASSWD: /bin/mount -t cifs //*/* /media/* -o username=*
    • 3

  4. A general solution to these issues is to put the following preamble at the top of your sudo requiring scripts:

    #!/bin/bash
case $EUID in
   0) : cool we are already root - fall through ;;
   *) # not root, become root for the rest of this session
      # (and ask for the sudo password only once)
      sudo $0 "$@" ;;
esac
# now the present process is effective-UID  (root)
# so there's no need to put sudo in front of commands

any more commands here will run as superuser ...

    Obviously, this has a downside in that if some commands in the script don't require sudo to run, there's an unnecessary elevation of privileges here.

    Anyway, thought I would share this little tip. The nicest thing about it, is that if you're already effective-uid root (e.g. if you already called it under sudo) it gracefully does the right thing. Also giving an error and forcing you to retype/rerun (with sudo) is less friendly.

    You may also want to check out the timestamp_timeout variable in man 5 sudoers which tells sudo to remember user credentials for a limited number of minutes (and can be fractional).

    • 1