[MCL-17439] The launcher crashes when filling a command block with this symbol: ■

The bug

If you fill a command block with ■ then the launcher crashes. The game itself (Java) remains open. It's easiest to notice the launcher crashing if you have the launcher log open, but if the launcher log is closed, you can still observe the launcher crashing by using Task Manager on windows or Activity Monitor on macOS.

To reproduce

Enable the launcher log in the launcher settings.
Launch Minecraft. (I've tested this in 1.16.5 and 21w11a.)
```
/give @p minecraft:command_block
```
Paste this symbol into the command block several times: ■
Use ctrl + a on windows or cmd + a on macOS to select all of the text in the command block.
Use ctrl + c on windows or cmd + c on macOS to copy all of the text.
Use ctrl + v on windows or cmd + v on macOS to paste the text again. Paste several copies of the text.
Repeat steps 5 through 7. This will exponentially fill up the command block. Stop repeating steps 5 through 7 when the command block is full.
Click "Done".
The launcher crashes. ❌

Attachments

Comments 5

pine1needle 2021-03-25T21:55:35Z

I discovered this while testing MC-220067.

[Mod] markderickson 2021-03-25T21:58:57Z

Can confirm in 2.2.2530.

pine1needle 2021-03-26T00:29:53Z

I assume that this happens on windows too, but I have not tested it. I would appreciate it if a windows user could test this and leave a comment so that I can either add the windows launcher version to the affected versions field, or else edit the description of the report.

migrated 2022-02-24T14:58:47Z

The reason why this happens is probably because the chunk buffer is too short, and it runs into Minecraft Launcher's RAM, possibly triggering CWE-121.

migrated 2022-02-24T14:59:10Z

I did not experience the launcher crash at all, likely because the buffer itself wasn't too short,