uucore: add O_NOFOLLOW to DirFd::open_file_at - #13623
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openat anchors the directory, not the final component, so open_file_at (O_CREAT|O_WRONLY|O_TRUNC) still followed a symlink planted at `name` and truncated its target -- despite the caller documenting the fd-based path as the one that "prevents symlink race conditions". install's copy_file_safe calls it immediately after unlink_at(), which is exactly the window an attacker races; the path-based copy_file is stricter here because create_new(true) implies O_EXCL. Truncate-an-existing-file semantics are unchanged; only symlinks are refused.
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openat anchors the directory, not the final component, so open_file_at (O_CREAT|O_WRONLY|O_TRUNC) still followed a symlink planted at
nameand truncated its target -- despite the caller documenting the fd-based path as the one that "prevents symlink race conditions".install's copy_file_safe calls it immediately after unlink_at(), which is exactly the window an attacker races; the path-based copy_file is stricter here because create_new(true) implies O_EXCL.
Truncate-an-existing-file semantics are unchanged; only symlinks are refused.