From: Thomas Jarosch thomas.jarosch@intra2net.com
[ Upstream commit b97df039a68b2f3e848e238df5d5d06343ea497b ]
Kernel 5.14 added a new "byseq" index to speed up xfrm_state lookups by sequence number in commit fe9f1d8779cb ("xfrm: add state hashtable keyed by seq")
While the patch was thorough, the function pfkey_send_new_mapping() in net/af_key.c also modifies x->km.seq and never added the current xfrm_state to the "byseq" index.
This leads to the following kernel Ooops: BUG: kernel NULL pointer dereference, address: 0000000000000000 .. RIP: 0010:__xfrm_state_delete+0xc9/0x1c0 .. Call Trace: <TASK> xfrm_state_delete+0x1e/0x40 xfrm_del_sa+0xb0/0x110 [xfrm_user] xfrm_user_rcv_msg+0x12d/0x270 [xfrm_user] ? remove_entity_load_avg+0x8a/0xa0 ? copy_to_user_state_extra+0x580/0x580 [xfrm_user] netlink_rcv_skb+0x51/0x100 xfrm_netlink_rcv+0x30/0x50 [xfrm_user] netlink_unicast+0x1a6/0x270 netlink_sendmsg+0x22a/0x480 __sys_sendto+0x1a6/0x1c0 ? __audit_syscall_entry+0xd8/0x130 ? __audit_syscall_exit+0x249/0x2b0 __x64_sys_sendto+0x23/0x30 do_syscall_64+0x3a/0x90 entry_SYSCALL_64_after_hwframe+0x61/0xcb
Exact location of the crash in __xfrm_state_delete(): if (x->km.seq) hlist_del_rcu(&x->byseq);
The hlist_node "byseq" was never populated.
The bug only triggers if a new NAT traversal mapping (changed IP or port) is detected in esp_input_done2() / esp6_input_done2(), which in turn indirectly calls pfkey_send_new_mapping() *if* the kernel is compiled with CONFIG_NET_KEY and "af_key" is active.
The PF_KEYv2 message SADB_X_NAT_T_NEW_MAPPING is not part of RFC 2367. Various implementations have been examined how they handle the "sadb_msg_seq" header field:
- racoon (Android): does not process SADB_X_NAT_T_NEW_MAPPING - strongswan: does not care about sadb_msg_seq - openswan: does not care about sadb_msg_seq
There is no standard how PF_KEYv2 sadb_msg_seq should be populated for SADB_X_NAT_T_NEW_MAPPING and it's not used in popular implementations either. Herbert Xu suggested we should just use the current km.seq value as is. This fixes the root cause of the oops since we no longer modify km.seq itself.
The update of "km.seq" looks like a copy'n'paste error from pfkey_send_acquire(). SADB_ACQUIRE must indeed assign a unique km.seq number according to RFC 2367. It has been verified that code paths involving pfkey_send_acquire() don't cause the same Oops.
PF_KEYv2 SADB_X_NAT_T_NEW_MAPPING support was originally added here: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
commit cbc3488685b20e7b2a98ad387a1a816aada569d8 Author: Derek Atkins derek@ihtfp.com AuthorDate: Wed Apr 2 13:21:02 2003 -0800
[IPSEC]: Implement UDP Encapsulation framework.
In particular, implement ESPinUDP encapsulation for IPsec Nat Traversal.
A note on triggering the bug: I was not able to trigger it using VMs. There is one VPN using a high latency link on our production VPN server that triggered it like once a day though.
Link: https://github.com/strongswan/strongswan/issues/992 Link: https://lore.kernel.org/netdev/00959f33ee52c4b3b0084d42c430418e502db554.1652... Link: https://lore.kernel.org/netdev/20221027142455.3975224-1-chenzhihao@meizu.com...
Fixes: fe9f1d8779cb ("xfrm: add state hashtable keyed by seq") Reported-by: Roth Mark rothm@mail.com Reported-by: Zhihao Chen chenzhihao@meizu.com Tested-by: Roth Mark rothm@mail.com Signed-off-by: Thomas Jarosch thomas.jarosch@intra2net.com Acked-by: Antony Antony antony.antony@secunet.com Acked-by: Herbert Xu herbert@gondor.apana.org.au Signed-off-by: Steffen Klassert steffen.klassert@secunet.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/key/af_key.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/key/af_key.c b/net/key/af_key.c index 213287814328..95edcbedf6ef 100644 --- a/net/key/af_key.c +++ b/net/key/af_key.c @@ -3394,7 +3394,7 @@ static int pfkey_send_new_mapping(struct xfrm_state *x, xfrm_address_t *ipaddr, hdr->sadb_msg_len = size / sizeof(uint64_t); hdr->sadb_msg_errno = 0; hdr->sadb_msg_reserved = 0; - hdr->sadb_msg_seq = x->km.seq = get_acqseq(); + hdr->sadb_msg_seq = x->km.seq; hdr->sadb_msg_pid = 0;
/* SA */