From: Ilya Maximets i.maximets@ovn.org
[ Upstream commit 5ace7ef87f059d68b5f50837ef3e8a1a4870c36e ]
The push_nsh() action structure looks like this:
OVS_ACTION_ATTR_PUSH_NSH(OVS_KEY_ATTR_NSH(OVS_NSH_KEY_ATTR_BASE,...))
The outermost OVS_ACTION_ATTR_PUSH_NSH attribute is OK'ed by the nla_for_each_nested() inside __ovs_nla_copy_actions(). The innermost OVS_NSH_KEY_ATTR_BASE/MD1/MD2 are OK'ed by the nla_for_each_nested() inside nsh_key_put_from_nlattr(). But nothing checks if the attribute in the middle is OK. We don't even check that this attribute is the OVS_KEY_ATTR_NSH. We just do a double unwrap with a pair of nla_data() calls - first time directly while calling validate_push_nsh() and the second time as part of the nla_for_each_nested() macro, which isn't safe, potentially causing invalid memory access if the size of this attribute is incorrect. The failure may not be noticed during validation due to larger netlink buffer, but cause trouble later during action execution where the buffer is allocated exactly to the size:
BUG: KASAN: slab-out-of-bounds in nsh_hdr_from_nlattr+0x1dd/0x6a0 [openvswitch] Read of size 184 at addr ffff88816459a634 by task a.out/22624
CPU: 8 UID: 0 PID: 22624 6.18.0-rc7+ #115 PREEMPT(voluntary) Call Trace: <TASK> dump_stack_lvl+0x51/0x70 print_address_description.constprop.0+0x2c/0x390 kasan_report+0xdd/0x110 kasan_check_range+0x35/0x1b0 __asan_memcpy+0x20/0x60 nsh_hdr_from_nlattr+0x1dd/0x6a0 [openvswitch] push_nsh+0x82/0x120 [openvswitch] do_execute_actions+0x1405/0x2840 [openvswitch] ovs_execute_actions+0xd5/0x3b0 [openvswitch] ovs_packet_cmd_execute+0x949/0xdb0 [openvswitch] genl_family_rcv_msg_doit+0x1d6/0x2b0 genl_family_rcv_msg+0x336/0x580 genl_rcv_msg+0x9f/0x130 netlink_rcv_skb+0x11f/0x370 genl_rcv+0x24/0x40 netlink_unicast+0x73e/0xaa0 netlink_sendmsg+0x744/0xbf0 __sys_sendto+0x3d6/0x450 do_syscall_64+0x79/0x2c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e </TASK>
Let's add some checks that the attribute is properly sized and it's the only one attribute inside the action. Technically, there is no real reason for OVS_KEY_ATTR_NSH to be there, as we know that we're pushing an NSH header already, it just creates extra nesting, but that's how uAPI works today. So, keeping as it is.
Fixes: b2d0f5d5dc53 ("openvswitch: enable NSH support") Reported-by: Junvy Yang zhuque@tencent.com Signed-off-by: Ilya Maximets i.maximets@ovn.org Acked-by: Eelco Chaudron echaudro@redhat.com Reviewed-by: Aaron Conole aconole@redhat.com Link: https://patch.msgid.link/20251204105334.900379-1-i.maximets@ovn.org Signed-off-by: Jakub Kicinski kuba@kernel.org (cherry picked from commit 5ace7ef87f059d68b5f50837ef3e8a1a4870c36e) Signed-off-by: Adrian Yip adrian.ytw@gmail.com --- net/openvswitch/flow_netlink.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c index e3359e15aa2e..7d5490ea23e1 100644 --- a/net/openvswitch/flow_netlink.c +++ b/net/openvswitch/flow_netlink.c @@ -2802,13 +2802,20 @@ static int validate_and_copy_set_tun(const struct nlattr *attr, return err; }
-static bool validate_push_nsh(const struct nlattr *attr, bool log) +static bool validate_push_nsh(const struct nlattr *a, bool log) { + struct nlattr *nsh_key = nla_data(a); struct sw_flow_match match; struct sw_flow_key key;
+ /* There must be one and only one NSH header. */ + if (!nla_ok(nsh_key, nla_len(a)) || + nla_total_size(nla_len(nsh_key)) != nla_len(a) || + nla_type(nsh_key) != OVS_KEY_ATTR_NSH) + return false; + ovs_match_init(&match, &key, true, NULL); - return !nsh_key_put_from_nlattr(attr, &match, false, true, log); + return !nsh_key_put_from_nlattr(nsh_key, &match, false, true, log); }
/* Return false if there are any non-masked bits set. @@ -3388,7 +3395,7 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr, return -EINVAL; } mac_proto = MAC_PROTO_NONE; - if (!validate_push_nsh(nla_data(a), log)) + if (!validate_push_nsh(a, log)) return -EINVAL; break;