regression: can't create socket

[ruv]

When tmux is started without options it produces the following error:

can't create socket: Permission denied

The TMUX_TMPDIR,TMPDIR, or -L option don't change this effect.

Although it runs normal with proper -S option.
This regression is observed in version 2.0 and 2.1 on Cygwin at the least.

[nicm]

Something is broken on your system, probably /tmp permissions.

-------- Original message --------
From: ruv notifications@github.com
Date:04/11/2015 19:24 (GMT+00:00)
To: tmux/tmux tmux@noreply.github.com
Subject: [tmux] regression: can't create socket (#180)

When tmux is started without options it produces the following error:

can't create socket: Permission denied
The TMUX_TMPDIR,TMPDIR, or -L option don't change this effect.

Although it runs normal with proper -S option.
This regression is observed in version 2.0 and 2.1 on Cygwin at the least.

—
Reply to this email directly or view it on GitHub.

[ruv]

This issue has appeared after update of Cygwin (i.e., when tmux version was updated). So, it worked well on the previous version of tmux (I didn't remark what was the version exactly).

Also note that my Cygwin is configured to use noacl option for all the mounts. Consequently, it is impossible to get permission denied error for writing into /tmp.

One possible reason is that if tmux tries to change some permissions and then checks whether they are changed. In case of noacl option the permissions cannot be changed. Could it be the problem for tmux?

[ruv]

I guess that the issue is in the following code of makesocketpath function:

if (sb.st_uid != uid || (sb.st_mode & S_IRWXO) != 0) {
    errno = EACCES;
    return (NULL);
}

The suspect commit: d451502

[nicm]

It is important that the socket directory is owned by you and not accessible by everyone, or any user could use your tmux server. For a while, tmux incorrectly skipped the access mode check, this was fixed in 2.0. If your system doesn't support creating directories in /tmp with the right ownership, you will have to use -S to point it explicitly to a socket. The check is important and we are not going to support systems that do not have Unix file permission semantics.

[ruv]

Thanks for clarification.
See also workaround for the same issue in MSYS environment. Maybe it is reasonable to introduce something like TMUX_NOACL environment variable for optionally skip the check in such specific cases.

[nicm]

I don't think we need anything like that, adding an environment variable
to bypass a security check is probably a poor choice. -S allows to get
around the problem in any case.

On Wed, Nov 04, 2015 at 03:05:08PM -0800, ruv wrote:

Thanks for clarification.
See also [1]workaround for the same issue in MSYS environment. Maybe it
reasonable to introduce something like TMUX_NOACL environment variable for
optionally skip the check in such specific cases.

--
Reply to this email directly or [2]view it on GitHub.

Reverse link: [3]unknown

References

Visible links

1. file:///Modify "can't create socket" occurred msys2/MSYS2-packages#286
2. regression: can't create socket #180 (comment)
3. regression: can't create socket #180 (comment)

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