Re: Bad leaks file fd to child processes

[Alexey]

On 2022-11-26 14:05, "凋叶棕" via Bug reports for the GNU Bourne Again 
SHell wrote:
> Hello,
>
> I find that the file descriptor leaks when I execute the command pvs
> in bash 5.2, The abnormal scenario is similar to the bug which
> reported by
> http://lists.gnu.org/archive/html/bug-bash/2017-01/msg00026.html
>
> When I execute pvs in the terminal opened through xshell，it’s ok
>
> PV         VG      Fmt  Attr PSize    PFree
> /dev/sda2  euleros lvm2 a--  <126.00g    0
>
> But when I execute pvs in the terminal opened through vscode（use
> Remote-SHH to connect linux）, the File descriptor was leaked
>
> File descriptor 19 (/dev/ptmx) leaked on pvs invocation. Parent PID
> 3789: /usr/bin/bash
> File descriptor 20 (/dev/ptmx) leaked on pvs invocation. Parent PID
> 3789: /usr/bin/bash
> File descriptor 21 (/dev/ptmx) leaked on pvs invocation. Parent PID
> 3789: /usr/bin/bash
> File descriptor 99
> (/root/.vscode-server/bin/899d46d82c4c95423fb7e10e68eba52050e30ba3/vscode-remote-lock.root.899d46d82c4c95423fb7e10e68eba52050e30ba3)
> leaked on pvs invocation. Parent PID 3789: /usr/bin/bash
>   PV         VG      Fmt  Attr PSize    PFree
>   /dev/sda2  euleros lvm2 a--  <126.00g    0
>
> I found that the leaked file descriptor was created in subst.c
>
> /* Pipe the output of executing STRING into the current shell. */
> if (pipe(fildes) < 0)
> {
>     sys_error("%s", _("cannot make pipe for command substitution"));
>     goto error_exit;
> }
>
> add it leaked in
>
> if (--bufn <= 0)
> {
>     SET_CLOSE_ON_EXEC(fd);
>     bufn = zread(fd, buf, sizeof(buf));
>     if (bufn <= 0)
>         break;
>     bufp = buf;
> }
>
> I try to add SET_CLOSE_ON_EXEC (fd) before zread, but it doesn't seem 
> to work.

Same behavior was in bash 4.4 (as well as now in bash 5.2):

# echo $BASH_VERSION
4.4.0(1)-release
# exec 66</etc/hosts
# pvs
File descriptor 66 (/etc/hosts) leaked on pvs invocation. Parent PID 
1057606: ./bash

But we use the fact tat bash doesn't close FD for example to preliminary 
open log file for utility that we will `exec' later.
Unfortunately bash doesn't provide any fcntl() mechanism to control FD 
flags.
It'll be great to have  ability to manage CLOEXEC or any other FD flags 
from the script.

Regards,
Alexey.