CVE-2023-53585
bpf: reject unhashed sockets in bpf_sk_assign
- Published
- Updated
- Reserved
- Assigned by
- Linux
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().
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| NVDNVD · Analyzed | 3.1 | Medium5.5 | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.16% · top 95% of all CVEs (7 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.5.
Affected products
- affected cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 – < 791a12102e5191dcb6ce0b3a99d71b5a2802d12a
- affected cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 – < 7dcbc0bb0e5cc1823923744befce59ac353135e6
- affected cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 – < c0ce0fb76610d5fad31f56f2ca8241a2a6717a1b
- affected cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 – < 8aa43cfbb68b25119d2ced14ec717173e2901fa2
- affected cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 – < 3d4522f59fb748a54446846522941a4f09da63e9
- affected cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 – < 67312adc96b5a585970d03b62412847afe2c6b01
- affected 5.7
- unaffected < 5.7
- unaffected 5.10.195 – ≤ 5.10.*
- unaffected 5.15.132 – ≤ 5.15.*
- unaffected 6.1.53 – ≤ 6.1.*
- unaffected 6.4.16 – ≤ 6.4.*
- unaffected 6.5.3 – ≤ 6.5.*
- unaffected 6.6 – ≤ *
References (6)
- https://git.kernel.org/stable/c/791a12102e5191dcb6ce0b3a99d71b5a2802d12a (opens in a new tab)
- https://git.kernel.org/stable/c/7dcbc0bb0e5cc1823923744befce59ac353135e6 (opens in a new tab)
- https://git.kernel.org/stable/c/c0ce0fb76610d5fad31f56f2ca8241a2a6717a1b (opens in a new tab)
- https://git.kernel.org/stable/c/8aa43cfbb68b25119d2ced14ec717173e2901fa2 (opens in a new tab)
- https://git.kernel.org/stable/c/3d4522f59fb748a54446846522941a4f09da63e9 (opens in a new tab)
- https://git.kernel.org/stable/c/67312adc96b5a585970d03b62412847afe2c6b01 (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
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[](https://trackcve.app/cve/CVE-2023-53585)Record last updated .