UBUNTU-CVE-2026-90110: Medium severity ubuntu/linux-azure vulnerability

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 gcstack 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 inetpeer 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 netgetrandomonce(). 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 inetpeer and compute the target hash (dhash) once at the beginning of inetgetpeer() to avoid recomputing SipHash at every step of the RB-tree walk.