linux/net/netfilter, branch v6.17

netfilter: nf_tables: restart set lookup on base_seq change

2025-09-10T18:30:37Z

The hash, hash_fast, rhash and bitwise sets may indicate no result even though a matching element exists during a short time window while other cpu is finalizing the transaction. This happens when the hash lookup/bitwise lookup function has picked up the old genbit, right before it was toggled by nf_tables_commit(), but then the same cpu managed to unlink the matching old element from the hash table: cpu0 cpu1 has added new elements to clone has marked elements as being inactive in new generation perform lookup in the set enters commit phase: A) observes old genbit increments base_seq I) increments the genbit II) removes old element from the set B) finds matching element C) returns no match: found element is not valid in old generation Next lookup observes new genbit and finds matching e2. Consider a packet matching element e1, e2. cpu0 processes following transaction: 1. remove e1 2. adds e2, which has same key as e1. P matches both e1 and e2. Therefore, cpu1 should always find a match for P. Due to above race, this is not the case: cpu1 observed the old genbit. e2 will not be considered once it is found. The element e1 is not found anymore if cpu0 managed to unlink it from the hlist before cpu1 found it during list traversal. The situation only occurs for a brief time period, lookups happening after I) observe new genbit and return e2. This problem exists in all set types except nft_set_pipapo, so fix it once in nft_lookup rather than each set ops individually. Sample the base sequence counter, which gets incremented right before the genbit is changed. Then, if no match is found, retry the lookup if the base sequence was altered in between. If the base sequence hasn't changed: - No update took place: no-match result is expected. This is the common case. or: - nf_tables_commit() hasn't progressed to genbit update yet. Old elements were still visible and nomatch result is expected, or: - nf_tables_commit updated the genbit: We picked up the new base_seq, so the lookup function also picked up the new genbit, no-match result is expected. If the old genbit was observed, then nft_lookup also picked up the old base_seq: nft_lookup_should_retry() returns true and relookup is performed in the new generation. This problem was added when the unconditional synchronize_rcu() call that followed the current/next generation bit toggle was removed. Thanks to Pablo Neira Ayuso for reviewing an earlier version of this patchset, for suggesting re-use of existing base_seq and placement of the restart loop in nft_set_do_lookup(). Fixes: 0cbc06b3faba ("netfilter: nf_tables: remove synchronize_rcu in commit phase") Signed-off-by: Florian Westphal

netfilter: nf_tables: make nft_set_do_lookup available unconditionally

2025-09-10T18:30:37Z

This function was added for retpoline mitigation and is replaced by a static inline helper if mitigations are not enabled. Enable this helper function unconditionally so next patch can add a lookup restart mechanism to fix possible false negatives while transactions are in progress. Adding lookup restarts in nft_lookup_eval doesn't work as nft_objref would then need the same copypaste loop. This patch is separate to ease review of the actual bug fix. Suggested-by: Pablo Neira Ayuso Signed-off-by: Florian Westphal

netfilter: nf_tables: place base_seq in struct net

2025-09-10T18:30:37Z

This will soon be read from packet path around same time as the gencursor. Both gencursor and base_seq get incremented almost at the same time, so it makes sense to place them in the same structure. This doesn't increase struct net size on 64bit due to padding. Signed-off-by: Florian Westphal

netfilter: nft_set_rbtree: continue traversal if element is inactive

2025-09-10T18:30:37Z

When the rbtree lookup function finds a match in the rbtree, it sets the range start interval to a potentially inactive element. Then, after tree lookup, if the matching element is inactive, it returns NULL and suppresses a matching result. This is wrong and leads to false negative matches when a transaction has already entered the commit phase. cpu0 cpu1 has added new elements to clone has marked elements as being inactive in new generation perform lookup in the set enters commit phase: I) increments the genbit A) observes new genbit B) finds matching range C) returns no match: found range invalid in new generation II) removes old elements from the tree C New nft_lookup happening now will find matching element, because it is no longer obscured by old, inactive one. Consider a packet matching range r1-r2: cpu0 processes following transaction: 1. remove r1-r2 2. add r1-r3 P is contained in both ranges. Therefore, cpu1 should always find a match for P. Due to above race, this is not the case: cpu1 does find r1-r2, but then ignores it due to the genbit indicating the range has been removed. It does NOT test for further matches. The situation persists for all lookups until after cpu0 hits II) after which r1-r3 range start node is tested for the first time. Move the "interval start is valid" check ahead so that tree traversal continues if the starting interval is not valid in this generation. Thanks to Stefan Hanreich for providing an initial reproducer for this bug. Reported-by: Stefan Hanreich Fixes: c1eda3c6394f ("netfilter: nft_rbtree: ignore inactive matching element with no descendants") Signed-off-by: Florian Westphal

netfilter: nft_set_pipapo: don't check genbit from packetpath lookups

2025-09-10T18:30:37Z

The pipapo set type is special in that it has two copies of its datastructure: one live copy containing only valid elements and one on-demand clone used during transaction where adds/deletes happen. This clone is not visible to the datapath. This is unlike all other set types in nftables, those all link new elements into their live hlist/tree. For those sets, the lookup functions must skip the new elements while the transaction is ongoing to ensure consistency. As the clone is shallow, removal does have an effect on the packet path: once the transaction enters the commit phase the 'gencursor' bit that determines which elements are active and which elements should be ignored (because they are no longer valid) is flipped. This causes the datapath lookup to ignore these elements if they are found during lookup. This opens up a small race window where pipapo has an inconsistent view of the dataset from when the transaction-cpu flipped the genbit until the transaction-cpu calls nft_pipapo_commit() to swap live/clone pointers: cpu0 cpu1 has added new elements to clone has marked elements as being inactive in new generation perform lookup in the set enters commit phase: I) increments the genbit A) observes new genbit removes elements from the clone so they won't be found anymore B) lookup in datastructure can't see new elements yet, but old elements are ignored -> Only matches elements that were not changed in the transaction II) calls nft_pipapo_commit(), clone and live pointers are swapped. C New nft_lookup happening now will find matching elements. Consider a packet matching range r1-r2: cpu0 processes following transaction: 1. remove r1-r2 2. add r1-r3 P is contained in both ranges. Therefore, cpu1 should always find a match for P. Due to above race, this is not the case: cpu1 does find r1-r2, but then ignores it due to the genbit indicating the range has been removed. At the same time, r1-r3 is not visible yet, because it can only be found in the clone. The situation persists for all lookups until after cpu0 hits II). The fix is easy: Don't check the genbit from pipapo lookup functions. This is possible because unlike the other set types, the new elements are not reachable from the live copy of the dataset. The clone/live pointer swap is enough to avoid matching on old elements while at the same time all new elements are exposed in one go. After this change, step B above returns a match in r1-r2. This is fine: r1-r2 only becomes truly invalid the moment they get freed. This happens after a synchronize_rcu() call and rcu read lock is held via netfilter hook traversal (nf_hook_slow()). Cc: Stefano Brivio Fixes: 3c4287f62044 ("nf_tables: Add set type for arbitrary concatenation of ranges") Signed-off-by: Florian Westphal

netfilter: nft_set_bitmap: fix lockdep splat due to missing annotation

2025-09-10T18:28:24Z

Running new 'set_flush_add_atomic_bitmap' test case for nftables.git with CONFIG_PROVE_RCU_LIST=y yields: net/netfilter/nft_set_bitmap.c:231 RCU-list traversed in non-reader section!! rcu_scheduler_active = 2, debug_locks = 1 1 lock held by nft/4008: #0: ffff888147f79cd8 (&nft_net->commit_mutex){+.+.}-{4:4}, at: nf_tables_valid_genid+0x2f/0xd0 lockdep_rcu_suspicious+0x116/0x160 nft_bitmap_walk+0x22d/0x240 nf_tables_delsetelem+0x1010/0x1a00 .. This is a false positive, the list cannot be altered while the transaction mutex is held, so pass the relevant argument to the iterator. Fixes tag intentionally wrong; no point in picking this up if earlier false-positive-fixups were not applied. Fixes: 28b7a6b84c0a ("netfilter: nf_tables: avoid false-positive lockdep splats in set walker") Signed-off-by: Florian Westphal

netfilter: nf_tables: Introduce NFTA_DEVICE_PREFIX

2025-09-04T07:19:25Z

This new attribute is supposed to be used instead of NFTA_DEVICE_NAME for simple wildcard interface specs. It holds a NUL-terminated string representing an interface name prefix to match on. While kernel code to distinguish full names from prefixes in NFTA_DEVICE_NAME is simpler than this solution, reusing the existing attribute with different semantics leads to confusion between different versions of kernel and user space though: * With old kernels, wildcards submitted by user space are accepted yet silently treated as regular names. * With old user space, wildcards submitted by kernel may cause crashes since libnftnl expects NUL-termination when there is none. Using a distinct attribute type sanitizes these situations as the receiving part detects and rejects the unexpected attribute nested in *_HOOK_DEVS attributes. Fixes: 6d07a289504a ("netfilter: nf_tables: Support wildcard netdev hook specs") Signed-off-by: Phil Sutter Signed-off-by: Florian Westphal

netfilter: conntrack: helper: Replace -EEXIST by -EBUSY

2025-08-27T09:53:38Z

The helper registration return value is passed-through by module_init callbacks which modprobe confuses with the harmless -EEXIST returned when trying to load an already loaded module. Make sure modprobe fails so users notice their helper has not been registered and won't work. Suggested-by: Christophe Leroy Fixes: 12f7a505331e ("netfilter: add user-space connection tracking helper infrastructure") Signed-off-by: Phil Sutter Signed-off-by: Florian Westphal

netfilter: nf_tables: reject duplicate device on updates

2025-08-13T06:34:55Z

A chain/flowtable update with duplicated devices in the same batch is possible. Unfortunately, netdev event path only removes the first device that is found, leaving unregistered the hook of the duplicated device. Check if a duplicated device exists in the transaction batch, bail out with EEXIST in such case. WARNING is hit when unregistering the hook: [49042.221275] WARNING: CPU: 4 PID: 8425 at net/netfilter/core.c:340 nf_hook_entry_head+0xaa/0x150 [49042.221375] CPU: 4 UID: 0 PID: 8425 Comm: nft Tainted: G S 6.16.0+ #170 PREEMPT(full) [...] [49042.221382] RIP: 0010:nf_hook_entry_head+0xaa/0x150 Fixes: 78d9f48f7f44 ("netfilter: nf_tables: add devices to existing flowtable") Fixes: b9703ed44ffb ("netfilter: nf_tables: support for adding new devices to an existing netdev chain") Signed-off-by: Pablo Neira Ayuso Signed-off-by: Florian Westphal

ipvs: Fix estimator kthreads preferred affinity

2025-08-13T06:34:33Z

The estimator kthreads' affinity are defined by sysctl overwritten preferences and applied through a plain call to the scheduler's affinity API. However since the introduction of managed kthreads preferred affinity, such a practice shortcuts the kthreads core code which eventually overwrites the target to the default unbound affinity. Fix this with using the appropriate kthread's API. Fixes: d1a89197589c ("kthread: Default affine kthread to its preferred NUMA node") Signed-off-by: Frederic Weisbecker Acked-by: Julian Anastasov Signed-off-by: Florian Westphal