netfilter: nf_conncount: fix zone comparison in tuple dedup

Overview

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

netfilter: nf_conncount: fix zone comparison in tuple dedup

The "already exists" dedup logic in __nf_conncount_add() decides whether a connection has already been counted and can be skipped instead of incrementing the connlimit count. It compares the conntrack zone of a list entry with the zone of the connection being added using nf_ct_zone_id() and nf_ct_zone_equal(), passing conn->zone.dir or zone->dir as the direction argument.

Those helpers take enum ip_conntrack_dir values: IP_CT_DIR_ORIGINAL is 0 and IP_CT_DIR_REPLY is 1. However, zone->dir is a u8 bitmask: NF_CT_ZONE_DIR_ORIG is 1, NF_CT_ZONE_DIR_REPL is 2 and NF_CT_DEFAULT_ZONE_DIR is 3. Passing that bitmask as the enum direction shifts the meaning of every non-zero value. An ORIG-only zone passes 1 and is tested as REPLY, while REPL-only and default zones pass 2 or 3 and test bits beyond the valid direction range. In those cases nf_ct_zone_id() can fall back to NF_CT_DEFAULT_ZONE_ID instead of using the real zone id, so different zones can be treated as equal and dedup collapses to tuple equality alone.

nf_conncount stores and compares the original-direction tuple for a connection. If an skb already has an attached conntrack entry, get_ct_or_tuple_from_skb() explicitly copies ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, regardless of the packet's ctinfo. Therefore the zone comparison in the tuple dedup path must use IP_CT_DIR_ORIGINAL as well; the zone direction bitmask describes where a zone id applies, not which direction this conncount tuple represents.

Fix the two dedup comparisons by passing IP_CT_DIR_ORIGINAL directly. Do not special-case NF_CT_DEFAULT_ZONE_DIR and do not compare raw zone ids: using the existing helpers with IP_CT_DIR_ORIGINAL preserves the direction-aware NF_CT_DEFAULT_ZONE_ID fallback. A default bidirectional zone contains the ORIG bit, so it naturally returns the real zone id; reply-only zones continue to fall back for original-direction tuple comparisons.

Affected

• Linux >= 21ba8847f857028dc83a0f341e16ecc616e34740 < 82fc35e0da9a91db9a034f8311f18f77a599ae3f
• Linux >= 21ba8847f857028dc83a0f341e16ecc616e34740 < 78b5d6dbc860776161f9e9206b06ff8a01f531ab
• Linux >= 21ba8847f857028dc83a0f341e16ecc616e34740 < 4f30a89c0ed2418719a1144881c2635b940b543d
• Linux >= 21ba8847f857028dc83a0f341e16ecc616e34740 < 7bdc3c0985ecf17b957811fedcc684acdf698acc
• Linux >= 21ba8847f857028dc83a0f341e16ecc616e34740 < 35a56e2a46b90e6bd4ca816b80e9cb8d20dfc3ce
• Linux >= 21ba8847f857028dc83a0f341e16ecc616e34740 < 3cd9a5792cbea81139c24320986dd0db69e9b5d0
• Linux >= 21ba8847f857028dc83a0f341e16ecc616e34740 < 6ff07ac5405bea4d4ead3559fc123f987576424a
• Linux >= 21ba8847f857028dc83a0f341e16ecc616e34740 < f62c41b4910e65da396ec9a8c40c1fe7fe82e449
• Linux 525e1dffed8711973f77412729621098a95238e5
• Linux 75af3d78168e654a5cd8bbc4c774f97be836165f
• Linux >= 4.14.92 < 4.15
• Linux 4.18

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.