Add a warning about the inter-qube clipboard maximum character limit

[qwrd]

The problem you're addressing (if any)

The inter-qube clipboard system appears to have a 65000 character limit, which means that any text longer than this limit that is copied between individual qubes by using the ctrl+shift+c and ctrl+shift+v shortcuts will be silently truncated to 65000 characters. I noticed this in Q4.2 while trying to copy over some config files from one GUI text editor to another in a different qube, and then some syntax errors appeared in the program log. Upon inspection, I noticed that a portion of the config file in the new qube was missing.

The solution you'd like

Please add some sort of warning message on the screen. When a user tries to copy a text section that is longer than this limit then a message should pop up notifying the user that not all text has been copied over.

The value to a user, and who that user might be

Any user who copies large portions of text won't wonder why some of it has disappeared.

Completion criteria checklist

(This section is for developer use only. Please do not modify it.)

[Solomon1732]

I offer that the warning also suggest the user instead copy files between qubes. Not that it will present a popup, but rather say the likes of "you can use use qvm-copy to copy large files between qubes."

[alimirjamali]

@marmarek I am looking at commit history to qubes-gui-daemon and in this specific commit from 2012, I can not find where the MAX_CLIPBOARD_SIZE is defined. Searching the repo does not provide any clue.

[marmarek]

https://github.com/QubesOS/qubes-gui-common/blob/main/include/qubes-gui-protocol.h#L86

[alimirjamali]

https://github.com/QubesOS/qubes-gui-common/blob/main/include/qubes-gui-protocol.h#L86

Thanks for the hint. Regardless of the OP, 65KB sound a little bit low (maybe even 12 years ago). This is less than 1000 at 40 chars width. Was there any security concern?

[alimirjamali]

After some consideration and study about this issue, it is not be simple. I could divide it to 4 (+1) individual sub-tasks:

• The 65000 character limit set 11 years ago by Rafal Wojtczuk should had been most probably due to X86 real-mode memory segmentation concerns. Which is no problem on X86-64 and is solved long ago. X11 could easily handle chunks of 256KiB or even higher nowadays before any necessity to switch to INCR. I guess it would be OK to increase the MAX_CLIPBOARD_SIZE to 256KiB. The current limit is too low.
• A patch to qubes-gui-daemon is necessary to raise proper errors instead of truncating the buffer.
• A patch to qubes-gui-agent-linux is necessary for protocol upgrade.
• An additional patch to Qubes Clipboard Widget is necessary for visual notification of error raised by GUI daemon.

[alimirjamali]

I offer that the warning also suggest the user instead copy files between qubes. Not that it will present a popup, but rather say the likes of "you can use use qvm-copy to copy large files between qubes."

For the task 2 & 3, instead of truncation which might result in data loss and corruption, a proper message could be raised as suggested above. But why not a popup? It could be a popup with this text:

Global Clipboard
Failed to fetch clipboard contents from qube: <b> {vmname> </b> !
Source content too big to fit in Global clipboard buffer.
Use `qvm-copy/qvm-move` to transfer large amount of data between qubes.
Global clipboard is wiped.

[alimirjamali]

PRs submitted (total of 5)

Review priority: Medium (since bug involves data loss)

Users could set the global clipboard limit via max_clipboard_size key within /etc/qubes/guid.conf. or via gui-default-max-clipboard-size feature of GUIVM (or dom0). Or can set limit per vm via gui-max-clipboard-size of individual qubes. The accepted values are between 256 characters to 256000 characters. Default is 64000 characters. Trying to copy sizes over it will trigger a Global Clipboard widget warning message and wipe the global clipboard. See video below:

clipboard.mp4