bluetooth socket sysinit: correct memset initialization

[rlibby]

Summary

gcc -Wmemset-elt-size diagnosed this. The code was only initializing
the first 1/sizeof(long) bytes. On 64-bit systems, this would mean only
events up to 0x20 were initialized.

This effectively reverses the security policy for some events with
higher ids, now permitting them on unprivileged sockets. Two that are
defined are NG_HCI_EVENT_LE (0x3e) and NG_HCI_EVENT_BT_LOGO (0xfe).

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I am not familiar with this code, am not planning to test bluetooth, and
am not in any rush to commit this, I just saw that this warning appeared
to be a genuine bug. I do not know what the appropriate security policy
actually is. Please feel free to take this patch over if desired.

Test Plan

make buildkernel

[markj]

Given that the next 70 lines are mostly manually setting bits in the mask, I'd err on the side of entirely removing this initialization.

[rlibby]

In D45707#1042749, @markj wrote:

Given that the next 70 lines are mostly manually setting bits in the mask, I'd err on the side of entirely removing this initialization.

It's actually only the next three operations that set bits in events. f is reassigned after that. So just removing the memset would be a change to permit no events on unprivileged sockets.

I do think that using default deny and explicit allows may be safer in general, though I don't know how much evolution of events there has been.

Anyway, I'm not invested enough in this code to go research events and implement something cleaner. Would it be better just to file a bugzilla bug for this?

[rlibby]

Filed https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=280039