CVE-2025-71160

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 is needed because chain loop detection also ensures we do not exceed the jump stack: Just because we know that j2 is cycle free, its last jump might now exceed the allowed stack size. We also need to update all reachable chains with the new largest observed call depth.

Care has to be taken to revalidate even if the chain depth won't be an issue: chain validation also ensures that expressions are not called from invalid base chains. For example, the masquerade expression can only be called from NAT postrouting base chains.

Therefore we also need to keep record of the base chain context (type, hooknum) and revalidate if the chain becomes reachable from a different hook location.

nf_tables may repeatedly re validate the same chain graph during a ruleset commit, which can result in excessive CPU usage and soft lockups in nft_chain_validate. PR:H is typical because modifying nftables rules requires CAP_NET_ADMIN in most deployments. The issue is not directly network reachable and is triggered through control plane rule updates rather than packet traffic. Impact is denial of service due to a stalled commit path and degraded system responsiveness.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.