Error not being raised when expected for unsafePath of `../upperfile.txt` about filepath-securejoin HOT 2 CLOSED

@vrothberg FYI

from filepath-securejoin.

I'll post a response both there and here -- the reasoning is that SecureJoin (which is soon going to be out-dated by libpathrs's path handling which is race-free) is effectively acting like a chroot. Thus /.. always becomes /.

This is necessary because there are lots of examples of malformed symlinks which only work because of this behaviour. If we made /.. cause an error, those symlinks wouldn't work -- and it's also unclear whether absolute symlinks should also trigger the error (in the podman build example, the symlink will be resolved differently to the host -- and this may be confusing to some users -- but on the other hand we absolutely need to allow absolute symlinks to work because many distributions use absolute symlinks all over the place).

We could work around this by making SecureJoin return an additional argument that says "you tried to cross the root" but I'm not really a huge fan of that idea -- aside from the fact that SecureJoin is going to be archived soon (once we switch enough people to libpathrs), it's also a bit of a weird thing for a caller to care about (though I do get why you'd want something like that).

I hasten to point out that docker build has the exact same semantics.

from filepath-securejoin.