CVE-2025-40254

Description

In the Linux kernel, the following vulnerability has been resolved:net: openvswitch: remove never-working support for setting nsh fieldsThe validation of the set(nsh(...)) action is completely wrong.It runs through the nsh_key_put_from_nlattr() function that is thesame function that validates NSH keys for the flow match and thepush_nsh() action. However, the set(nsh(...)) has a very differentmemory layout. Nested attributes in there are doubled in size incase of the masked set(). That makes proper validation impossible.There is also confusion in the code between the masked flag, thatsays that the nested attributes are doubled in size containing boththe value and the mask, and the is_mask that says that the valuewere parsing is the mask. This is causing kernel crash on trying towrite into mask part of the match with SW_FLOW_KEY_PUT() duringvalidation, while validate_nsh() doesnt allocate any memory for it: BUG: kernel null pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 1c2383067 P4D 1c2383067 PUD 20b703067 PMD 0 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 8 UID: 0 Kdump: loaded Not tainted 6.17.0-rc4+ #107 PREEMPT(voluntary) RIP: 0010:nsh_key_put_from_nlattr+0x19d/0x610 [openvswitch] Call Trace: validate_nsh+0x60/0x90 [openvswitch] validate_set.constprop.0+0x270/0x3c0 [openvswitch] __ovs_nla_copy_actions+0x477/0x860 [openvswitch] ovs_nla_copy_actions+0x8d/0x100 [openvswitch] ovs_packet_cmd_execute+0x1cc/0x310 [openvswitch] genl_family_rcv_msg_doit+0xdb/0x130 genl_family_rcv_msg+0x14b/0x220 genl_rcv_msg+0x47/0xa0 netlink_rcv_skb+0x53/0x100 genl_rcv+0x24/0x40 netlink_unicast+0x280/0x3b0 netlink_sendmsg+0x1f7/0x430 ____sys_sendmsg+0x36b/0x3a0 ___sys_sendmsg+0x87/0xd0 __sys_sendmsg+0x6d/0xd0 do_syscall_64+0x7b/0x2c0 entry_SYSCALL_64_after_hwframe+0x76/0x7eThe third issue with this process is that while trying to convertthe non-masked set into masked one, validate_set() copies and doublesthe size of the OVS_KEY_ATTR_NSH as if it didnt have any nestedattributes. It should be copying each nested attribute and doublingthem in size independently. And the process must be properly reversedduring the conversion back from masked to a non-masked variant duringthe flow dump.In the end, the only two outcomes of trying to use this action areeither validation failure or a kernel crash. And if somehow someonemanages to install a flow with such an action, it will most definitelynot do what it is supposed to, since all the keys and the masks aremixed up.Fixing all the issues is a complex task as it requires re-writingmost of the validation code.Given that and the fact that this functionality never worked sinceintroduction, lets just remove it altogether. Its better tore-introduce it later with a proper implementation instead of tryingto fix it in stable releases.

Risk Information

Associated Vulnerability

Patch Details

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234