问题
I was wondering how openssh gets the password when login, cause I got stuck in automating entering passwords to the similar tools in linux which requires getting password from tty like ssh.
Tried to understand sshpass and found that sshpass forks a child process with the same pid then enters the password under the child process.
Don't know if my guess was right that ssh needs to check the right pid since I cannot stdin to the current tty using another process to enter the ssh password.
回答1:
For security reasons, many programs requires a password interactively from users. Quite many programs uses the following kind of check before reading a password from stdin:
if (isatty(STDIN_FILENO) == 0)
{
exit(EXIT_FAILURE);
}
So the program allows password only from a terminal. That way it try to prevent non-interactive password entering.
sshpass is just a tool for:
fooling ssh into thinking it is getting the password from an interactive user. [from man page of sshpass]
For fooling ssh, sshpass creates and open a pseudo terminal, and gives that for stdin of ssh. fork() is needed because sshpass must write a password to ssh via the pseudo terminal.
This way stdin of ssh process is a terminal, and isatty test will be passed.
来源：https://stackoverflow.com/questions/55351259/how-does-ssh-receive-password-from-tty