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CLOSE_RANGE_CLOEXEC marks a range close-on-exec. Nothing happens to these fds unless an exec happens. Add CLOSE_RANGE_CLOEXEC_ONLY which closes the close-on-exec file descriptors in the range. When combined with CLOSE_RANGE_EXCEPT it names the close-on-exec file descriptors that are supposed to survive. Every close-on-exec fd outside of the range is closed. File descriptors without that flag are left alone. Whatever the caller deliberately passes down, stdio, LISTEN_FDS, an inherited pipe, remains where it is. The handful of close-on-exec descriptors the caller still needs for the exec such as the executable, an error pipe, sit in a specific range. That is what a task between clone(CLONE_FILES) and execve() actually wants: clone(CLONE_FILES | CLONE_VM | CLONE_VFORK) child: close_range(lo, hi, CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC_ONLY | CLOSE_RANGE_EXCEPT) child: rearrange descriptors in the now private table child: execve() Between the clone and the close_range() the child holds no reference of its own on any file because copy_files() only bumps the fdtable refcount. So a close() in the parent takes effect immediately. The unshare also never takes a reference on the fds it leaves behind either. The range is expressed in the parent's numbering. So a caller that cannot name the file descriptors it keeps contiguously picks a range wide enough to cover them, unshares, and tidies up with a second close_range() on the table it now owns alone. That one is cheap. To keep nothing, name a range that cannot hold an open descriptor, e.g. close_range(~0U, ~0U, ...). CLOSE_RANGE_CLOEXEC and CLOSE_RANGE_CLOEXEC_ONLY are mutually exclusive. Link: https://patch.msgid.link/20260921-work-file-close_range_except-v1-9-c20d0b49270d@kernel.org Reviewed-by: Jann Horn <jannh@google.com> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org> |
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