CVE-2024-50130

In the Linux kernel, the following vulnerability has been resolved:

netfilter: bpf: must hold reference on net namespace

BUG: KASAN: slab-use-after-free in _nfunregisternethook+0x640/0x6b0 Read of size 8 at addr ffff8880106fe400 by task repro/72= bpfnflinkrelease+0xda/0x1e0 bpflinkfree+0x139/0x2d0 bpflinkrelease+0x68/0x80 _fput+0x414/0xb60

Eric says: It seems that bpf was able to defer the _nfunregisternethook() after exit()/close() time. Perhaps a netns reference is missing, because the netns has been dismantled/freed already. bpfnflink_attach() does : link->net = net; But I do not see a reference being taken on net.

Add such a reference and release it after hook unreg. Note that I was unable to get syzbot reproducer to work, so I do not know if this resolves this splat.