netfilter: nft_tunnel: fix geneve_opt type confusion addition
CVE: CVE-2025-22056
Component: kernel
CWE: CWE-787
Severity: Moderate
CVSS v3: 7.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Release date: 2025-04-16T00:00:00+00:00

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

netfilter: nft_tunnel: fix geneve_opt type confusion addition

When handling multiple NFTA_TUNNEL_KEY_OPTS_GENEVE attributes, the
parsing logic should place every geneve_opt structure one by one
compactly. Hence, when deciding the next geneve_opt position, the
pointer addition should be in units of char *.

However, the current implementation erroneously does type conversion
before the addition, which will lead to heap out-of-bounds write.

[    6.989857] ==================================================================
[    6.990293] BUG: KASAN: slab-out-of-bounds in nft_tunnel_obj_init+0x977/0xa70
[    6.990725] Write of size 124 at addr ffff888005f18974 by task poc/178
[    6.991162]
[    6.991259] CPU: 0 PID: 178 Comm: poc-oob-write Not tainted 6.1.132 #1
[    6.991655] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
[    6.992281] Call Trace:
[    6.992423]  <TASK>
[    6.992586]  dump_stack_lvl+0x44/0x5c
[    6.992801]  print_report+0x184/0x4be
[    6.993790]  kasan_report+0xc5/0x100
[    6.994252]  kasan_check_range+0xf3/0x1a0
[    6.994486]  memcpy+0x38/0x60
[    6.994692]  nft_tunnel_obj_init+0x977/0xa70
[    6.995677]  nft_obj_init+0x10c/0x1b0
[    6.995891]  nf_tables_newobj+0x585/0x950
[    6.996922]  nfnetlink_rcv_batch+0xdf9/0x1020
[    6.998997]  nfnetlink_rcv+0x1df/0x220
[    6.999537]  netlink_unicast+0x395/0x530
[    7.000771]  netlink_sendmsg+0x3d0/0x6d0
[    7.001462]  __sock_sendmsg+0x99/0xa0
[    7.001707]  ____sys_sendmsg+0x409/0x450
[    7.002391]  ___sys_sendmsg+0xfd/0x170
[    7.003145]  __sys_sendmsg+0xea/0x170
[    7.004359]  do_syscall_64+0x5e/0x90
[    7.005817]  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
[    7.006127] RIP: 0033:0x7ec756d4e407
[    7.006339] Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 faf
[    7.007364] RSP: 002b:00007ffed5d46760 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
[    7.007827] RAX: ffffffffffffffda RBX: 00007ec756cc4740 RCX: 00007ec756d4e407
[    7.008223] RDX: 0000000000000000 RSI: 00007ffed5d467f0 RDI: 0000000000000003
[    7.008620] RBP: 00007ffed5d468a0 R08: 0000000000000000 R09: 0000000000000000
[    7.009039] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
[    7.009429] R13: 00007ffed5d478b0 R14: 00007ec756ee5000 R15: 00005cbd4e655cb8

Fix this bug with correct pointer addition and conversion in parse
and dump code.

Statement: The config param CONFIG_NFT_TUNNEL disabled before the latest version of the Red Hat Enterprise Linux 9, so actual only starting from 9.6. For the Red Hat Enterprise Linux 8 not affected.

Only local users with `CAP_NET_ADMIN` capability or root can trigger this issue. 
On Red Hat Enterprise Linux, local unprivileged users can exploit unprivileged user namespaces (CONFIG_USER_NS) to grant themselves this capability.

The OpenShift Container Platform (OCP) control planes or master machines are based on Red Hat Enterprise Linux CoreOS (RHCOS) that consists primarily of RHEL components, therefore, it is also affected by this kernel vulnerability. A successful exploit needs necessary privileges (CAP_NET_ADMIN) and direct, local access. A local user in RHCOS is already a root with full permissions, hence existence of this vulnerability does not bring any value from the potential attacker perspective. From the OpenShift containers perspective, this vulnerability cannot be exploited as in OpenShift the cluster processes on the node are namespaced, which means that switching the namespace in the running OpenShift container will not bring necessary capabilities.
This means that for OpenShift, the impact of this vulnerability is Low.

Similar to the CVE-2023-32233 vulnerability, this has been explained in the following blog post as an example of a "Container escape vulnerability":
https://www.redhat.com/en/blog/containers-vulnerability-risk-assessment

Remediation:
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
1. This flaw can be mitigated by preventing the affected netfilter module with the name nft_tunnel from being loaded. For instructions on how to blacklist a kernel module, please see https://access.redhat.com/solutions/41278.

2. If the module cannot be disabled, on non-containerized deployments of Red Hat Enterprise Linux, the mitigation is to disable user namespaces:

# echo "user.max_user_namespaces=0" > /etc/sysctl.d/userns.conf
# sysctl -p /etc/sysctl.d/userns.conf
On containerized deployments, such as Red Hat OpenShift Container Platform, do not use the second mitigation (disabling user namespaces) as the functionality is needed to be enabled. The first mitigation (blacklisting nf_tables) is still viable for containerized deployments, providing the environment is not using netfilter.