[Bug 256334] [genet] Race condition in Pi4's gen_attach() can cause SIGSEGV.

[b***@freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=256334

Bug ID: 256334
Summary: [genet] Race condition in Pi4's gen_attach() can cause
SIGSEGV.
Product: Base System
Version: CURRENT
Hardware: arm64
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: arm
Assignee: freebsd-***@FreeBSD.org
Reporter: ***@blackberry.com

'genet' driver starts interrupt handlers before ifp is allocated.

Version: git main @ d3f7975fcb346ea28dde079a9c04cff5ef20a8d7

gen_intr() uses sc->ifp here:
https://cgit.freebsd.org/src/blame/sys/arm64/broadcom/genet/if_genet.c#n1260

gen_attach() calls bus_setup_intr() here:
https://cgit.freebsd.org/src/blame/sys/arm64/broadcom/genet/if_genet.c#n283
https://cgit.freebsd.org/src/blame/sys/arm64/broadcom/genet/if_genet.c#n290

gen_attach() calls if_alloc() here:
https://cgit.freebsd.org/src/blame/sys/arm64/broadcom/genet/if_genet.c#n298

Possible fixes:
gen_attach() could either hold GEN_LOCK() or complete the init before the
bus_setup_intr() calls.