Affected: Linux

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

netfilter: nf_tables: avoid chain re-validation if possible

Hamza Mahfooz reports cpu soft lock-ups in nft_chain_validate():

watchdog: BUG: soft lockup - CPU#1 stuck for 27s! [iptables-nft-re:37547] [..] RIP: 0010:nft_chain_validate+0xcb/0x110 [nf_tables] [..] nft_immediate_validate+0x36/0x50 [nf_tables] nft_chain_validate+0xc9/0x110 [nf_tables] nft_immediate_validate+0x36/0x50 [nf_tables] nft_chain_validate+0xc9/0x110 [nf_tables] nft_immediate_validate+0x36/0x50 [nf_tables] nft_chain_validate+0xc9/0x110 [nf_tables] nft_immediate_validate+0x36/0x50 [nf_tables] nft_chain_validate+0xc9/0x110 [nf_tables] nft_immediate_validate+0x36/0x50 [nf_tables] nft_chain_validate+0xc9/0x110 [nf_tables] nft_immediate_validate+0x36/0x50 [nf_tables] nft_chain_validate+0xc9/0x110 [nf_tables] nft_table_validate+0x6b/0xb0 [nf_tables] nf_tables_validate+0x8b/0xa0 [nf_tables] nf_tables_commit+0x1df/0x1eb0 [nf_tables] [..]

Currently nf_tables will traverse the entire table (chain graph), starting from the entry points (base chains), exploring all possible paths (chain jumps). But there are cases where we could avoid revalidation.

Consider: 1 input -> j2 -> j3 2 input -> j2 -> j3 3 input -> j1 -> j2 -> j3

Then the second rule does not need to revalidate j2, and, by extension j3, because this was already checked during validation of the first rule. We need to validate it only for rule 3.

This…