mkdirall regression with filepath.MkdirAll

[cyphar]

This may causes a regression for dind now. @cyphar

@lifubang ➜ ~/ubuntu $ sudo /workspaces/runc/runc create test
ERRO[0000] runc create failed: unable to start container process: error during container init: error mounting "proc" to rootfs at "/proc": possible attack detected: newly created directory "/home/codespace/ubuntu/rootfs/proc" has incorrect mode 0o42755 (expected 0o40755)

This is from github codespace online webide, I think it looks like a dind, and it worked before.

Originally posted by @lifubang in #4393 (comment)