Openat2

openat2 Resolve Flags Constrain Path Traversal During Lookup

A pathname passed to openat() is resolved by the kernel, but the caller has limited control over traversal through intermediate components. Linux openat2() adds a resolve field that applies constraints to the complete lookup operation. The restriction is evaluated while components are traversed, rather than by validating a pathname in userspace and opening it later. That distinction matters when path components can change concurrently. A userspace sequence that checks a path and then opens it creates separate observations of mutable filesystem state. openat2() places the selected lookup policy in the same system call that returns the file descriptor.