Linux Keyboard Permission Issue "Fix It" Button Doesn't Work

[rjhilgefort]

Describe the bug
On the development build, the "Fix It" button gave me an error that looks like permission issues.

I was chatting with @obra on Discord and that conversation can be seen here:
https://discord.com/channels/492408953041321984/638783537734090813/775867293196484609

To Reproduce
Steps to reproduce the behavior:

1. Download development build
2. Click on "Fix It" related to udev rules

Expected behavior
I suppose I expected it to resolve the permission issue it claimed to say it would fix.

Screenshots

Desktop (please complete the following information):

• OS: Arch 5.9.6
• Chrysalis Version: 0.7.9+286

Additional context
N/A

[algernon]

I guess Arch is not using udev and/or systemd?

[obra]

can we detect the failure we ran into and point people at a webpage? possibly showing the user which device you need access to, what it’s permissions are and What group you would need to be in to be able to access it. On the theory that if the smart way to do it has failed Users probably need to resort to getting into the correct group

…

On Nov 11, 2020, at 2:01 PM, Gergely Nagy ***@***.***> wrote:  I guess Arch is not using udev and/or systemd? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub, or unsubscribe.

[algernon]

We can, yes. We can't (easily) detect the exact error, but we can direct them to a page when we encounter any error. Apart from authentication, we can detect that, and we shouldn't direct them anywhere in that case.

[kurzkopfgleitbeutler]

I get the same issue with Chrysalis-0.8.0.amd64.AppImage on Ubuntu 20.04.1 LTS.

cd "/home/foo/chrysalis";
"/usr/bin/pkexec" --disable-internal-agent /bin/bash -c "echo SUDOPROMPT;
(mv /etc/udev/rules.d/60-kaleidoscope.rules /etc/udev/rules.d/60-kaleidoscope.rules.orig || true)
&& cp /tmp/.mount_ChrysaxM57yH/resources/static/udev/60-kaleidoscope.rules /etc/udev/rules.d/
&& udevadm control --reload-rules
&& udevadm trigger /dev/ttyACM0"

mv: cannot stat '/etc/udev/rules.d/60-kaleidoscope.rules': No such file or directory
cp: cannot stat '/tmp/.mount_ChrysaxM57yH/resources/static/udev/60-kaleidoscope.rules': Permission denied

From the error, I'd guess it has to do with how permissions in AppImage are handled. Maybe (n.b. I don't know about this kind of stuff) it has to do with chromium sandboxing or preserving ownership in the AppImage, does this have to do with it?
laurent22/joplin#2246 (comment)

[hatxet]

@kurzkopfgleitbeutler I get the same error as you, also on Ubuntu 20.04 LTS. That temporary mount folder in /tmp sure doesn't look right.

root@localhost# ls -la /tmp/                                                                                                                                                   
d?????????  ? ?     ?          ?            ?  .mount_ChrysatuM5zq/  

root@localhost# ls -l /tmp/.mount_ChrysatuM5zq                                                                                                                                                                      
ls: cannot access '/tmp/.mount_ChrysatuM5zq': Permission denied

[algernon]

I think I figured out what the problem is. It looks like the temporary mount folder is set up so that it is only accessible to the process that created it - which makes sense, and @kurzkopfgleitbeutler's assumption seems to be correct. This means that we can't copy files out of it after we elevated our privileges to root. As such, the solution is most likely to copy the file without elevating privileges to a place where we can copy (or rather, move) from as root. Therefore, we need to copy the udev rules file to a temporary place first, without elevated privileges, and then move it from there after, as root.

[algernon]

Reproduced, fix tested & pushed to master.