CVE-2023-53585

Description

In the Linux kernel, the following vulnerability has been resolved: bpf: reject unhashed sockets in bpf_sk_assign The semantics for bpf_sk_assign are as follows: sk = some_lookup_func() bpf_sk_assign(skb, sk) bpf_sk_release(sk) That is, the sk is not consumed by bpf_sk_assign. The function therefore needs to make sure that sk lives long enough to be consumed from __inet_lookup_skb. The path through the stack for a TCPv4 packet is roughly: netif_receive_skb_core: takes RCU read lock __netif_receive_skb_core: sch_handle_ingress: tcf_classify: bpf_sk_assign() deliver_ptype_list_skb: deliver_skb: ip_packet_type->func == ip_rcv: ip_rcv_core: ip_rcv_finish_core: dst_input: ip_local_deliver: ip_local_deliver_finish: ip_protocol_deliver_rcu: tcp_v4_rcv: __inet_lookup_skb: skb_steal_sock The existing helper takes advantage of the fact that everything happens in the same RCU critical section: for sockets with SOCK_RCU_FREE set bpf_sk_assign never takes a reference. skb_steal_sock then checks SOCK_RCU_FREE again and does sock_put if necessary. This approach assumes that SOCK_RCU_FREE is never set on a sk between bpf_sk_assign and skb_steal_sock, but this invariant is violated by unhashed UDP sockets. A new UDP socket is created in TCP_CLOSE state but without SOCK_RCU_FREE set. That flag is only added in udp_lib_get_port() which happens when a socket is bound. When bpf_sk_assign was added it wasn't possible to access unhashed UDP sockets from BPF, so this wasn't a problem. This changed in commit 0c48eefae712 ("sock_map: Lift socket state restriction for datagram sockets"), but the helper wasn't adjusted accordingly. The following sequence of events will therefore lead to a refcount leak: 1. Add socket(AF_INET, SOCK_DGRAM) to a sockmap. 2. Pull socket out of sockmap and bpf_sk_assign it. Since SOCK_RCU_FREE is not set we increment the refcount. 3. bind() or connect() the socket, setting SOCK_RCU_FREE. 4. skb_steal_sock will now set refcounted = false due to SOCK_RCU_FREE. 5. tcp_v4_rcv() skips sock_put(). Fix the problem by rejecting unhashed sockets in bpf_sk_assign(). This matches the behaviour of __inet_lookup_skb which is ultimately the goal of bpf_sk_assign().

Gravité et risque d'exploitation

CVE-2023-53585 obtient un score CVSS de 0.0/10, soit une gravité non évaluée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.16 %, ce qui la place devant 4.3 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=6.1.*, 0, <7dcbc0bb0e5cc1823923744befce59ac353135e6, <791a12102e5191dcb6ce0b3a99d71b5a2802d12a, <8aa43cfbb68b25119d2ced14ec717173e2901fa2, <5.7, 6.5.3, <=5.10.*, 6.4.16, 6.6, <3d4522f59fb748a54446846522941a4f09da63e9, <c0ce0fb76610d5fad31f56f2ca8241a2a6717a1b, <67312adc96b5a585970d03b62412847afe2c6b01, 5.15.132, 5.7, 5.10.195, <=*, <=5.15.*, <=6.5.*, cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449, 6.1.53, <=6.4.*) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/791a12102e5191dcb6ce0b3a99d71b5a2802d12a
• https://git.kernel.org/stable/c/7dcbc0bb0e5cc1823923744befce59ac353135e6
• https://git.kernel.org/stable/c/c0ce0fb76610d5fad31f56f2ca8241a2a6717a1b
• https://git.kernel.org/stable/c/8aa43cfbb68b25119d2ced14ec717173e2901fa2
• https://git.kernel.org/stable/c/3d4522f59fb748a54446846522941a4f09da63e9
• https://git.kernel.org/stable/c/67312adc96b5a585970d03b62412847afe2c6b01