> If the shell would expand the contents of PS1 when drawing the prompt, a raw ref name must not be included in PS1. This protects the user from arbitrary code execution via specially crafted ref names. For example, a ref named 'refs/heads/$(IFS=_;cmd=sudo_rm_-rf_/;$cmd)' might cause the shell to execute 'sudo rm -rf /' when the prompt is drawn.

[1]: https://github.com/git/git/blob/9d77b0405ce6b471cb5ce3a90436...

That code appears to be written by someone named Richard Hansen. I don't even see Linus in the git blame output of that file.