Linux Security

Cybersecurity 17 Sep 2026 7 min read

fs-verity Makes File Data Integrity a Read-Time Property

A host may need to keep independently updated executables, packages, models, or data on a writable filesystem while still detecting modification of file contents after an artifact has been accepted. A one-time userspace hash can identify the bytes at one moment, but it does not make later reads depend on that measurement. The file may be opened again, pages may be evicted and reloaded, and storage below the page cache may return different data.

Cybersecurity Linux Security

Cybersecurity 17 Sep 2026 5 min read

execveat Binds Program Execution to an Open File Reference

A launcher selects an executable from a directory, checks attributes or content, and then starts it. If selection and execution each resolve the pathname independently, a rename, symlink change, or directory replacement between those operations can make the executed object differ from the object that was checked. Linux execveat() can move that boundary from a second pathname lookup to an already acquired file reference. With AT_EMPTY_PATH, an empty pathname tells the kernel to execute the object referred to by dirfd. That descriptor may have been opened with O_PATH. The execution decision still passes through normal kernel permission and executable-format checks, but object selection no longer depends on resolving the original pathname again.

Cybersecurity Linux Security

Cybersecurity 17 Sep 2026 5 min read

Close-on-Exec Makes Descriptor Inheritance an Explicit Boundary

A service opens a privileged socket, starts helper programs, and expects those helpers to receive only standard input, output, and error. One descriptor created without close-on-exec can quietly violate that boundary. If it remains present when a new program image is installed, the helper inherits access to the kernel object even when its own credentials could never have opened that object. Linux treats this as descriptor inheritance, not a new authorization event. The security decision made when the object was opened is embodied in the descriptor. FD_CLOEXEC controls whether that established authority crosses a successful execve().

Cybersecurity Linux Security