netfilter: bpf: must hold reference on net namespace

Vulnerability Description

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 __nf_unregister_net_hook+0x640/0x6b0 Read of size 8 at addr ffff8880106fe400 by task repro/72= bpf_nf_link_release+0xda/0x1e0 bpf_link_free+0x139/0x2d0 bpf_link_release+0x68/0x80 __fput+0x414/0xb60 Eric says: It seems that bpf was able to defer the __nf_unregister_net_hook() after exit()/close() time. Perhaps a netns reference is missing, because the netns has been dismantled/freed already. bpf_nf_link_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.

References

• https://git.kernel.org/stable/c/f41bd93b3e0508edc7ba820357f949071dcc0acc
• https://git.kernel.org/stable/c/d0d7939543a1b3bb93af9a18d258a774daf8f162
• https://git.kernel.org/stable/c/1230fe7ad3974f7bf6c78901473e039b34d4fb1f