mod-orphan

Linux networking modules that were removed from the kernel tree because nobody maintained them and they had too many bugs, kept here as out-of-tree modules so that the people who still use them can keep running them.

This repository is also where the AX.25, NET/ROM and ROSE fixes are developed, reviewed and merged before they are sent to the stable and long-term kernels that still carry these protocols in-tree.

Contents

Subsystem	Modules	Removed from the kernel by
Amateur radio	ax25, netrom, rose, and the drivers 6pack, baycom_*, bpqether, hdlcdrv, mkiss, scc, yam	commit 32bb4a38e352 ("net: remove amateur radio (hamradio) subsystem")
ATM	clip, lec, mpoa and the PCI/SBUS drivers (ATM core, PPPoA, br2684, solos-pci and the USB DSL drivers went back in-tree)	commit c29fbdee0b9d ("net: remove ATM networking subsystem")
ISDN	mISDN_core, mISDN_dsp, l1oip, the mISDN hardware drivers, kernelcapi and Bluetooth cmtp	commit afee2aa98a00 ("net: remove ISDN subsystem and Bluetooth CMTP")
AppleTalk	appletalk (DDP, AARP)	removal of the AppleTalk protocol

The code is the in-tree code at the time of removal, with only the changes needed to build outside the tree. Each import commit lists these changes. Examples: dev->ax25_ptr and dev->atalk_ptr no longer exist in struct net_device, so the modules keep their own lists, and local copies of the removed headers are used instead of the kernel's.

Building

You need the headers or the build tree of the kernel you run.

make                          # against the running kernel
make KDIR=/path/to/kernel     # against another kernel tree
sudo make install             # modules_install, then: sudo depmod -a
make clean

include/hamradio_compat.h supplies helpers that are missing from older kernels, so the same sources also build on kernels that still have the subsystems in-tree (6.12.y, 6.18.y, 7.0). The modules built here then replace the in-tree ones, which is how the AX.25 fixes are tested on live networks before they reach a stable release.

Always build on the machine that will load the modules, or against the exact build tree of its kernel: a matching uname -r alone is not enough to guarantee a compatible module.

AppleTalk needs CONFIG_LLC in the host kernel (see net/appletalk/Kbuild).

Amateur radio: AX.25, NET/ROM and ROSE

What AX.25 is

AX.25 is the link layer protocol of amateur packet radio. It was derived from X.25 by radio amateurs in the early 1980s and standardised as AX.25 version 2.0 in 1984. Each station is identified by its callsign, and frames can be relayed by other stations ("digipeaters"). With AX.25, amateur radio operators send messages, files and data by radio, without any commercial network:

• on VHF and UHF, most often at 1200 bit/s (AFSK) or 9600 bit/s (G3RUH FSK), and on HF at lower speeds;
• through amateur satellites and the International Space Station: the PACSAT store-and-forward satellites, and the APRS digipeaters in orbit;
• with APRS (Automatic Packet Reporting System), which sends position reports, weather data and short messages in AX.25 frames;
• through bulletin board systems (BBS) that forward personal messages and bulletins between themselves around the world.

Above AX.25, NET/ROM and ROSE add a network layer, so that a user can reach a distant station across a chain of nodes:

• NET/ROM builds its routes automatically from the broadcasts of neighbouring nodes;
• ROSE (X.25 packet layer protocol over AX.25) routes calls by address, much like the X.25 public data networks it was derived from. Its addresses use an X.121 numbering plan (DNIC + area + node).

AX.25 and the Internet

AX.25 was tied to the Internet from the beginning. IP over AX.25 has worked since the mid-1980s (notably with Phil Karn's KA9Q NOS), ARP has a hardware type for AX.25, and since 1981 radio amateurs have had their own IPv4 address block, 44.0.0.0/8 (AMPRNet). So TCP/IP has run on radio links for decades, and packet radio networks are linked to each other over the Internet: AX.25 frames are carried in UDP or IP datagrams (ax25ipd, bpqether on Ethernet), which lets nodes on different continents talk as if they were neighbours on the air.

Linux has supported AX.25 almost since its first releases. It includes NET/ROM and ROSE sockets, KISS interfaces (mkiss, 6pack), interfaces for the classic packet radio cards (scc, baycom, yam), and AX.25 over Ethernet (bpqether). The user space side is the ax25-tools and ax25-apps packages, with programs such as kissattach, ax25d, ax25ipd, netromd and call. On top of these run full node and BBS packages such as FPAC (ROSE/NET/ROM node) and LinFBB (BBS).

Where the AX.25 fixes come from

Many amateur radio networks run on Linux, from Raspberry Pi nodes at home to gateways linking whole countries. The ROSE and NET/ROM networks connected to the F6BVP nodes in France, and their links abroad, depend directly on these kernel modules.

When the amateur radio subsystem was removed from the kernel because of its bug count, the bugs did not go away for the people who use it. Since May 2026, Bernard Pidoux, F6BVP, a long-time contributor to the Linux ROSE code and to the FPAC node software, has used this repository to fix them. The fixes:

• come from failures seen on real packet radio links and from syzbot reports: reference leaks, use-after-free, races at module removal and on device shutdown, ROSE circuits that are never released, AX.25 links that stall after a retransmission, unchecked frame lengths in AX.25 and NET/ROM;
• run for days on a live network of eight Linux nodes (Raspberry Pi and PC, kernels 5.4 to 7.0) with real packet radio traffic before they are proposed;
• are reviewed here as pull requests and merged into main;
• are then picked up by the stable maintainers for the long-term kernels that still contain these protocols (6.12.y and 6.18.y).

To see which stable and long-term releases already contain each fix, and when they reach Raspberry Pi kernels, see http://f6bvp.org/kernels-lts.html (French: http://f6bvp.org/noyaux-lts.html). That page is updated automatically.

Contributing

• Open a pull request against main, one fix per commit, with a commit message in the kernel style: subsystem: summary, an explanation of the bug and of the fix, Fixes: when relevant, and Signed-off-by:.
• For amateur radio, say how the fix was tested, and if possible test it on a real link or with realistic traffic.
• Discussion of the amateur radio protocols takes place on the linux-hams mailing list (linux-hams@vger.kernel.org).

License

GPL-2.0, like the Linux kernel code these modules come from. See the SPDX headers in each file.