kernel/git/next/linux-next.git/net/ipv4/inetpeer.c, branch stable

inetpeer: randomize RB-tree node comparison using SipHash

2026-08-20T19:55:31+00:00

The inetpeer rate limiting system stores peer entries in a Red-Black tree keyed deterministically on the remote IP address. Because tree lookups walk the RB-tree using standard lexicographical comparisons (inetpeer_addr_cmp), an off-path adversary can predict the exact topology of the tree and the sequence of nodes traversed during lookups (the gc_stack candidate list). By combining deterministic tree traversal with aggressive garbage collection (triggered when tree size exceeds inet_peer_threshold), an attacker can selectively force the eviction of targeted inet_peer nodes. When an evicted node is subsequently re-created upon receiving a new packet, its rate-limiting token bucket (rate_tokens, rate_last) is reset to full capacity. This creates a side-channel primitive allowing off-path attackers to bypass IP-keyed ICMP rate limits and infer open UDP ports (similar to SAD DNS style attacks). Mitigate this by randomizing the RB-tree node comparison logic using SipHash with a secret key (inetpeer_hash_key) initialized via net_get_random_once(). Nodes are ordered in the tree by SipHash(addr, key) rather than raw IP addresses. Because the secret key is unknown to external entities, the tree layout and lookup traversal paths are unpredictable to off-path adversaries, breaking the deterministic eviction gadget. Cache the computed 64-bit SipHash (hash) in struct inet_peer and compute the target hash (dhash) once at the beginning of inet_getpeer() to avoid recomputing SipHash at every step of the RB-tree walk. Fixes: b145425f269a ("inetpeer: remove AVL implementation in favor of RB tree") Reported-by: Michael Blunt Suggested-by: Michael Blunt Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260818151213.3953963-1-edumazet@google.com Signed-off-by: Jakub Kicinski

inetpeer: add a missing read_seqretry() in inet_getpeer()

2026-05-07T00:44:13+00:00

When performing a lockless lookup over the inet_peer rbtree, if a matching node is found, inet_getpeer() returns it immediately without validating the seqlock sequence. This missing check introduces a race condition: Trigger Path: When a host receives an incoming fragmented IPv4 packet, ip4_frag_init() (in net/ipv4/ip_fragment.c) calls inet_getpeer_v4() to track the peer. The Race: If the packet is from a new source IP, CPU A acquires the write_seqlock, allocates a new inet_peer node (p), sets its IP address (daddr), and links it to the rbtree (rb_link_node). Uninitialized Access: Due to the lack of memory barriers between rb_link_node and the initialization of the rest of the struct (like refcount_set(&p->refcnt, 1)), CPU A can make the node visible to readers before its refcnt is initialized. This is especially true on weakly-ordered architectures like ARM64 where the CPU can reorder the memory stores. Lockless Reader: Concurrently, CPU B processes a second fragmented packet from the same source IP. CPU B does a lockless lookup, finds the newly inserted node, and returns it immediately. Use-After-Free (UAF): CPU B reads p->refcnt as uninitialized garbage (left over from previous kmalloc-128/192 allocations). If the garbage is > 0, refcount_inc_not_zero(&p->refcnt) succeeds. CPU A then executes refcount_set(&p->refcnt, 1), overwriting CPU B's increment. When CPU B finishes with the fragment queue, it calls inet_putpeer(), which drops the refcount to 0 and frees the node via RCU. The node is now freed but remains linked in the rbtree, resulting in a Use-After-Free in the rbtree. Fixes: b145425f269a ("inetpeer: remove AVL implementation in favor of RB tree") Reported-by: Damiano Melotti Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260505133233.3039575-1-edumazet@google.com Signed-off-by: Jakub Kicinski

net: remove EXPORT_IPV6_MOD() and EXPORT_IPV6_MOD_GPL() macros

2026-03-29T18:21:22+00:00

As IPv6 is built-in only, the macro is always evaluating to an empty one. Remove it completely from the code. Signed-off-by: Fernando Fernandez Mancera Link: https://patch.msgid.link/20260325120928.15848-3-fmancera@suse.de Signed-off-by: Jakub Kicinski

net: Add SPDX ids to some source files

2026-03-10T01:32:45+00:00

Add SPDX-License-Identifier lines to several source files under the network sub-directory. Work on files in the core, dns_resolver, ipv4, ipv6 and netfilter sub-dirs. Remove boilerplate and license reference text to avoid ambiguity. Rusty Russell has expressed that his contributions were intended to be GPL-2.0-or-later. Signed-off-by: Tim Bird Link: https://patch.msgid.link/20260305004724.87469-1-tim.bird@sony.com Signed-off-by: Jakub Kicinski

inetpeer: use EXPORT_IPV6_MOD[_GPL]()

2025-02-14T21:09:39+00:00

Use EXPORT_IPV6_MOD[_GPL]() for symbols that do not need to to be exported unless CONFIG_IPV6=m Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Reviewed-by: Mateusz Polchlopek Link: https://patch.msgid.link/20250212132418.1524422-3-edumazet@google.com Signed-off-by: Jakub Kicinski

inetpeer: avoid false sharing in inet_peer_xrlim_allow()

2024-12-20T21:04:40+00:00

Under DOS, inet_peer_xrlim_allow() might be called millions of times per second from different cpus. Make sure to write over peer->rate_tokens and peer->rate_last only when really needed. Note the inherent races of this function are still there, we do not care of precise ICMP rate limiting. Signed-off-by: Eric Dumazet Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20241219150330.3159027-1-edumazet@google.com Signed-off-by: Jakub Kicinski

inetpeer: do not get a refcount in inet_getpeer()

2024-12-18T03:37:48+00:00

All inet_getpeer() callers except ip4_frag_init() don't need to acquire a permanent refcount on the inetpeer. They can switch to full RCU protection. Move the refcount_inc_not_zero() into ip4_frag_init(), so that all the other callers no longer have to perform a pair of expensive atomic operations on a possibly contended cache line. inet_putpeer() no longer needs to be exported. After this patch, my DUT can receive 8,400,000 UDP packets per second targeting closed ports, using 50% less cpu cycles than before. Also change two calls to l3mdev_master_ifindex() by l3mdev_master_ifindex_rcu() (Ido ideas) Fixes: 8c2bd38b95f7 ("icmp: change the order of rate limits") Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20241215175629.1248773-5-edumazet@google.com Signed-off-by: Jakub Kicinski

inetpeer: update inetpeer timestamp in inet_getpeer()

2024-12-18T03:37:00+00:00

inet_putpeer() will be removed in the following patch, because we will no longer use refcounts. Update inetpeer timestamp (p->dtime) at lookup time. Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20241215175629.1248773-4-edumazet@google.com Signed-off-by: Jakub Kicinski

inetpeer: remove create argument of inet_getpeer()

2024-12-18T03:37:00+00:00

All callers of inet_getpeer() want to create an inetpeer. Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20241215175629.1248773-3-edumazet@google.com Signed-off-by: Jakub Kicinski

inetpeer: replace call_rcu by kfree_rcu for simple kmem_cache_free callback

2024-10-15T17:50:21+00:00

Since SLOB was removed and since commit 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"), it is not necessary to use call_rcu when the callback only performs kmem_cache_free. Use kfree_rcu() directly. The changes were made using Coccinelle. Signed-off-by: Julia Lawall Reviewed-by: Eric Dumazet Acked-by: Paul E. McKenney Acked-by: Vlastimil Babka Link: https://patch.msgid.link/20241013201704.49576-4-Julia.Lawall@inria.fr Signed-off-by: Jakub Kicinski