Prevent file descriptor leak in the spawned child

After forking the child process, the file descriptors for the master and
slave aren't closed since we created these descriptors ourselves (Rust
sets CLOEXEC on any fds created in the stdlib).

Signed-off-by: Kieran Siek <[email protected]>

Author: kosayoda

src/process.rs

@@ -7,7 +7,7 @@ use nix::libc::{STDERR_FILENO, STDIN_FILENO, STDOUT_FILENO};
 use nix::pty::{grantpt, posix_openpt, unlockpt, PtyMaster};
 pub use nix::sys::{signal, wait};
 use nix::sys::{stat, termios};
-use nix::unistd::{dup, dup2, fork, setsid, ForkResult, Pid};
+use nix::unistd::{close, dup, dup2, fork, setsid, ForkResult, Pid};
 use std;
 use std::fs::File;
 use std::os::unix::io::{AsRawFd, FromRawFd};
@@ -97,6 +97,9 @@ impl PtyProcess {
 
         match unsafe { fork()? } {
             ForkResult::Child => {
+                // Avoid leaking master fd
+                close(master_fd.as_raw_fd())?;
+
                 setsid()?; // create new session with child as session leader
                 let slave_fd = open(
                     std::path::Path::new(&slave_name),
@@ -109,6 +112,11 @@ impl PtyProcess {
                 dup2(slave_fd, STDOUT_FILENO)?;
                 dup2(slave_fd, STDERR_FILENO)?;
 
+                // Avoid leaking slave fd
+                if slave_fd > STDERR_FILENO {
+                    close(slave_fd)?;
+                }
+
                 // set echo off
                 let mut flags = termios::tcgetattr(STDIN_FILENO)?;
                 flags.local_flags &= !termios::LocalFlags::ECHO;