CVE-2026-90110

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

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 (inetpeeraddrcmp),

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 inetpeerthreshold), 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 (ratetokens, ratelast) 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 (inetpeerhashkey) initialized via netgetrandom_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.