Patching the default PATH of `su`

Patching the default PATH of `su`

[Leo Famulari]

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In the man page of su(1), it says this:

------
The current environment is passed to the new shell. The value of $PATH is reset to
/bin:/usr/bin for normal users, or /sbin:/bin:/usr/sbin:/usr/bin for the superuser.
This may be changed with the ENV_PATH and ENV_SUPATH definitions in /etc/login.defs.
------

This means that `su leo` or `sudo su` give a broken environment on
GuixSD. You have to use `su --login` instead.

Should we use our own values for ENV_PATH and ENV_SUPATH so that this
works out of the box?

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Re: Patching the default PATH of `su`

[Ludovic Courtès]

Hello,

Leo Famulari <leo@famulari.name> skribis:

> In the man page of su(1), it says this:
>
> ------
> The current environment is passed to the new shell. The value of $PATH is reset to
> /bin:/usr/bin for normal users, or /sbin:/bin:/usr/sbin:/usr/bin for the superuser.
> This may be changed with the ENV_PATH and ENV_SUPATH definitions in /etc/login.defs.
> ------
>
> This means that `su leo` or `sudo su` give a broken environment on
> GuixSD. You have to use `su --login` instead.
>
> Should we use our own values for ENV_PATH and ENV_SUPATH so that this
> works out of the box?

Probably, yes.  It would be good to check how this affects
mingetty/login, sshd, etc.

Note that libc also has its own default PATH value in <paths.h>:

  /* Default search path. */
  #define	_PATH_DEFPATH	"/usr/bin:/bin"
  /* All standard utilities path. */
  #define	_PATH_STDPATH \
          "/usr/bin:/bin:/usr/sbin:/sbin"

Does ‘su’ rely on this?  In a future rebuild cycle we could change these
values, but /run/current-system/bin wouldn’t work on foreign distros, so
it’s not clear there’s much to gain.

Thanks,
Ludo’.

Re: Patching the default PATH of `su`

[Leo Famulari]

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On Fri, Apr 06, 2018 at 10:01:57AM +0200, Ludovic Courtès wrote:
> Probably, yes.  It would be good to check how this affects
> mingetty/login, sshd, etc.

Okay. I can test the change.

> Note that libc also has its own default PATH value in <paths.h>:
> 
>   /* Default search path. */
>   #define	_PATH_DEFPATH	"/usr/bin:/bin"
>   /* All standard utilities path. */
>   #define	_PATH_STDPATH \
>           "/usr/bin:/bin:/usr/sbin:/sbin"
> 
> Does ‘su’ rely on this?  In a future rebuild cycle we could change these
> values, but /run/current-system/bin wouldn’t work on foreign distros, so
> it’s not clear there’s much to gain.

I don't think `su` uses this, but I'll find out. As you say, it wouldn't
help much on foreign distros. I think the situation with `su` is
different, since it seems inconvenient to use our `su` on a foreign
distro, because it needs to be setuid.

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