Zellij leaks file descriptors to the running processes/shell

[tailhook]

Basic information

zellij --version: 0.8.1
tput lines: irrelevant
tput cols: irrelevant
uname -av or ver(Windows): Linux nixos 5.14.10 #1-NixOS SMP Thu Oct 7 05:53:20 UTC 2021 x86_64 GNU/Linux
alacritty --version: alacritty 0.9.0

Further information
Here is what I get in lsof -p $$ of the shell started from zellij:

zsh     189291   pc    0u   CHR              136,7       0t0      10 /dev/pts/7
zsh     189291   pc    1u   CHR              136,7       0t0      10 /dev/pts/7
zsh     189291   pc    2u   CHR              136,7       0t0      10 /dev/pts/7
zsh     189291   pc    5u  unix 0x0000000000000000       0t0   22962 /run/user/1000/zellij/0.18.1/session1 type=STREAM (LISTEN)
zsh     189291   pc    6u  unix 0x0000000000000000       0t0   22963 /run/user/1000/zellij/0.18.1/session1 type=STREAM (CONNECTED)
zsh     189291   pc    7u  unix 0x0000000000000000       0t0   22963 /run/user/1000/zellij/0.18.1/session1 type=STREAM (CONNECTED)
zsh     189291   pc    8u  unix 0x0000000000000000       0t0   22084 /run/user/1000/zellij/0.18.1/session1 type=STREAM (CONNECTED)
zsh     189291   pc    9u  unix 0x0000000000000000       0t0   22084 /run/user/1000/zellij/0.18.1/session1 type=STREAM (CONNECTED)
zsh     189291   pc   10u   CHR              136,7       0t0      10 /dev/pts/7
zsh     189291   pc   11u   CHR                5,2       0t0      85 /dev/ptmx
zsh     189291   pc   14u  unix 0x0000000000000000       0t0   22098 /run/user/1000/zellij/0.18.1/session1 type=STREAM (CONNECTED)
zsh     189291   pc   15u  unix 0x0000000000000000       0t0   22098 /run/user/1000/zellij/0.18.1/session1 type=STREAM (CONNECTED)
zsh     189291   pc   17r  FIFO               0,13       0t0  637219 pipe
zsh     189291   pc   18w  FIFO               0,13       0t0  637219 pipe
zsh     189291   pc   19u   CHR                5,2       0t0      85 /dev/ptmx
zsh     189291   pc   20u   CHR                5,2       0t0      85 /dev/ptmx
zsh     189291   pc   21u   CHR                5,2       0t0      85 /dev/ptmx

This is the same shell running from alacritty directly:

zsh     515006   pc    0u   CHR 136,12      0t0      15 /dev/pts/12
zsh     515006   pc    1u   CHR 136,12      0t0      15 /dev/pts/12
zsh     515006   pc    2u   CHR 136,12      0t0      15 /dev/pts/12
zsh     515006   pc   10u   CHR 136,12      0t0      15 /dev/pts/12

So unix sockets are clearly leaking to the child, but probably pipes and ptmx is too.

To fix it you have to either consistently set cloexec flag on all files/sockets or close all sockets after fork (by iterating from 3 to ulimit, or using closefrom/close_range on systems that support that). Preferably doing both, because cloexec saves from leaking to processes run by any method (say zellij use a library that spawns a process), and closing after fork saves you from libraries that use file descriptors but didn't implement cloexec.

[tailhook]

Looks like it's been addressed by #830