panic: mutex Giant not owned at src/sys/security/mac/mac_net.c:355

Hello

I have a reproduceable panic when I have MAC enabled in my kernel and I
try to run tcpdump on the interface I have logged in on via ssh (I'm not
really sure why it only happens in this case and in other cases).  I run
"tcpdump -n -i sis0" and the panic as shown below.  I do not have any
MAC policies loaded.

The problem is (if I understand the code correctly) that MAC calls
BPFD_LOCK_ASSERT, which rwatson added NET_ASSERT_GIANT to, but since the
sis interrupt handler is marked INTR_MPSAFE then GIANT isn't aquired
before bpf_mtap (and therefor mac_check_bpfdesc_receive) is called.

I'm not really sure what the correct fix is, but if bpf is locked, is
GIANT really required for it?

panic: mutex Giant not owned at /data/nanobsd/src/sys/security/mac/mac_net.c:355
at line 729 in file /data/nanobsd/src/sys/kern/kern_mutex.c
Debugger("panic")
Stopped at      Debugger+0x45:  xchgl   %ebx,in_Debugger.0
db> trace
Debugger(c063705f) at Debugger+0x45
__panic(c06363ea,2d9,c063655f,c063669a,c0646fff) at __panic+0xc7
_mtx_assert(c0689720,1,c0646fff,163) at _mtx_assert+0xc2
mac_check_bpfdesc_receive(c1995c00,c1750c00) at mac_check_bpfdesc_receive+0x40
bpf_mtap(c17536c0,c0adfa00) at bpf_mtap+0xa6
sis_start(c1750c00) at sis_start+0x1a7
sis_tick(c1750c00) at sis_tick+0x70
softclock(0) at softclock+0x176
ithread_loop(c0ac2500,c80c2d48,c0ac2500,c04c2e80,0) at ithread_loop+0x11c
fork_exit(c04c2e80,c0ac2500,c80c2d48) at fork_exit+0xa8
fork_trampoline() at fork_trampoline+0x8
--- trap 0x1, eip = 0, esp = 0xc80c2d7c, ebp = 0 ---

-- 
Simon L. Nielsen
FreeBSD Documentation Team