From 2ee66e9487172fcd189bc52a767c30dad7141c09 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 18 Aug 2026 15:12:13 +0000 Subject: inetpeer: randomize RB-tree node comparison using SipHash 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 --- include/net/inetpeer.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include') diff --git a/include/net/inetpeer.h b/include/net/inetpeer.h index f475757daafb..414e9adf4c51 100644 --- a/include/net/inetpeer.h +++ b/include/net/inetpeer.h @@ -35,6 +35,7 @@ struct inetpeer_addr { struct inet_peer { struct rb_node rb_node; + u64 hash; struct inetpeer_addr daddr; u32 metrics[RTAX_MAX]; @@ -125,6 +126,9 @@ static inline int inetpeer_addr_cmp(const struct inetpeer_addr *a, { int i, n; + if (a->family != b->family) + return a->family < b->family ? -1 : 1; + if (a->family == AF_INET) n = sizeof(a->a4) / sizeof(u32); else -- cgit v1.2.3