Before:
```
jail -c name=bug persist vnet
sysctl net.fibs=3
setfib 2 jexec bug ping -c 1 1.1.1
PING 1.1.1 (1.1.0.1): 56 data bytes
client_loop: send disconnect: Broken pipe
...
Fatal trap 12: page fault while in kernel mode
```
After:
```
jail -c name=bug persist vnet
sysctl net.fibs=3
setfib 2 jexec bug ping -c 1 1.1.1
jexec: jail_attach(1): Operation not permitted
```