The total size of the user-provided nmreq to nmreq_copyin() was first computed and then trusted during the copyin. This time-of-check to time-of-use bug could lead to kernel memory corruption. On systems configured to include netmap in their devfs_ruleset, a privileged process running in a jail can affect the host environment.
https://security.netapp.com/advisory/ntap-20240419-0003/
https://security.freebsd.org/advisories/FreeBSD-SA-22:04.netmap.asc