CVE-2021-47452

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> netfilter: nf_tables: skip netdev events generated on netns removal<br /> <br /> syzbot reported following (harmless) WARN:<br /> <br /> WARNING: CPU: 1 PID: 2648 at net/netfilter/core.c:468<br /> nft_netdev_unregister_hooks net/netfilter/nf_tables_api.c:230 [inline]<br /> nf_tables_unregister_hook include/net/netfilter/nf_tables.h:1090 [inline]<br /> __nft_release_basechain+0x138/0x640 net/netfilter/nf_tables_api.c:9524<br /> nft_netdev_event net/netfilter/nft_chain_filter.c:351 [inline]<br /> nf_tables_netdev_event+0x521/0x8a0 net/netfilter/nft_chain_filter.c:382<br /> <br /> reproducer:<br /> unshare -n bash -c &amp;#39;ip link add br0 type bridge; nft add table netdev t ; \<br /> nft add chain netdev t ingress \{ type filter hook ingress device "br0" \<br /> priority 0\; policy drop\; \}&amp;#39;<br /> <br /> Problem is that when netns device exit hooks create the UNREGISTER<br /> event, the .pre_exit hook for nf_tables core has already removed the<br /> base hook. Notifier attempts to do this again.<br /> <br /> The need to do base hook unregister unconditionally was needed in the past,<br /> because notifier was last stage where reg-&gt;dev dereference was safe.<br /> <br /> Now that nf_tables does the hook removal in .pre_exit, this isn&amp;#39;t<br /> needed anymore.