I am porting the driver for a USB device to Rocky Linux 9.3. Once the module is inserted, new logins by ssh are unresponsive. Blacklisting the module and rebooting restores normal functionality.
https://github.com/izot/lon-driver
With the module inserted, lsmod|grep u50 "Used By" goes from 0 to 1 about every 7 secs. Then, when an SSH login is attempted, Used By goes between 3 and 2.
Stop the SSH login, modprobe -r u50, try again...Now SSH gets motd but no prompt and says "PTY allocation request failed on channel 0."
ssh SITE "/bin/bash -i" (login succeeds) (same with module inserted)
modinfo u50
filename: /lib/modules/5.14.0-362.18.1.el9_3.x86_64/kernel/drivers/lon/u50.kodescription: U50 SMIP Driver 1.4 L2alias: tty-ldisc-28license: GPLrhelversion: 9.3srcversion: 311B898EC0CC268466EA85Bdepends:retpoline: Yname: u50vermagic: 5.14.0-362.18.1.el9_3.x86_64 SMP preempt mod_unload modversionsWith the module removed, journalctl shows "error: openpty: Cannot allocate memory" and "error: session_pty_req: session 0 alloc failed."
With the module inserted again and an SSH attempt, journalctl shows "NetworkManager ... manager: (lon10): new Generic device (/org/freedesktop/NetworkManager/Devices/743)" and "NetworkManager ... manager: (lon11): new Generic device (/org/freedesktop/NetworkManager/Devices/744)."
When the SSH attempt is canceled, journalctl shows "Removing a network device that was not added" twice.
I finally have gdb setup to remotely debug. I copied the src to the host running gdb. I can break at a function in the loadable module but that is too late. I need to break when the module is loaded and it kills new ssh logins. This module is for USB and is not related to ssh.
I can break at do_init_module() and step until exit_to_user_mode_loop() then it says "Cannot find bounds of current function." Setting a breakpoint at module_init() for a future load does not break.