CVE-2021-47452 Information

Description

In the Linux kernel the following vulnerability has been resolved:

netfilter: nf_tables: skip netdev events generated on netns removal

syzbot reported following (harmless) WARN:

WARNING: CPU: 1 PID: 2648 at net/netfilter/core.c:468 nft_netdev_unregister_hooks net/netfilter/nf_tables_api.c:230 [inline] nf_tables_unregister_hook include/net/netfilter/nf_tables.h:1090 [inline] __nft_release_basechain+0x138/0x640 net/netfilter/nf_tables_api.c:9524 nft_netdev_event net/netfilter/nft_chain_filter.c:351 [inline] nf_tables_netdev_event+0x521/0x8a0 net/netfilter/nft_chain_filter.c:382

reproducer: unshare -n bash -c ‘ip link add br0 type bridge; nft add table netdev t ;
nft add chain netdev t ingress \ type filter hook ingress device r0\
priority 0; policy drop; '

Problem is that when netns device exit hooks create the UNREGISTER event the .pre_exit hook for nf_tables core has already removed the base hook. Notifier attempts to do this again.

The need to do base hook unregister unconditionally was needed in the past because notifier was last stage where reg->dev dereference was safe.

Now that nf_tables does the hook removal in .pre_exit this isn’t needed anymore.

Reference

https://git.kernel.org/stable/c/90c7c58aa2bd02c65a4c63b7dfe0b16eab12cf9f https://git.kernel.org/stable/c/68a3765c659f809dcaac20030853a054646eb739