Re: [PATCH 1/1] selinux: netlabel: Prevent KMSAN warning in selinux_inet_conn_request()

[Paul Moore]

On Aug 15, 2023 Andrew Kanner <andrew.kanner@xxxxxxxxx> wrote:
> 
> KMSAN reports the following issue:
> [   81.822503] =====================================================
> [   81.823222] BUG: KMSAN: uninit-value in selinux_inet_conn_request+0x2c8/0x4b0
> [   81.823891]  selinux_inet_conn_request+0x2c8/0x4b0
> [   81.824385]  security_inet_conn_request+0xc0/0x160
> [   81.824886]  tcp_v4_route_req+0x30e/0x490
> [   81.825343]  tcp_conn_request+0xdc8/0x3400
> [   81.825813]  tcp_v4_conn_request+0x134/0x190
> [   81.826292]  tcp_rcv_state_process+0x1f4/0x3b40
> [   81.826797]  tcp_v4_do_rcv+0x9ca/0xc30
> [   81.827236]  tcp_v4_rcv+0x3bf5/0x4180
> [   81.827670]  ip_protocol_deliver_rcu+0x822/0x1230
> [   81.828174]  ip_local_deliver_finish+0x259/0x370
> [   81.828667]  ip_local_deliver+0x1c0/0x450
> [   81.829105]  ip_sublist_rcv+0xdc1/0xf50
> [   81.829534]  ip_list_rcv+0x72e/0x790
> [   81.829941]  __netif_receive_skb_list_core+0x10d5/0x1180
> [   81.830499]  netif_receive_skb_list_internal+0xc41/0x1190
> [   81.831064]  napi_complete_done+0x2c4/0x8b0
> [   81.831532]  e1000_clean+0x12bf/0x4d90
> [   81.831983]  __napi_poll+0xa6/0x760
> [   81.832391]  net_rx_action+0x84c/0x1550
> [   81.832831]  __do_softirq+0x272/0xa6c
> [   81.833239]  __irq_exit_rcu+0xb7/0x1a0
> [   81.833654]  irq_exit_rcu+0x17/0x40
> [   81.834044]  common_interrupt+0x8d/0xa0
> [   81.834494]  asm_common_interrupt+0x2b/0x40
> [   81.834949]  default_idle+0x17/0x20
> [   81.835356]  arch_cpu_idle+0xd/0x20
> [   81.835766]  default_idle_call+0x43/0x70
> [   81.836210]  do_idle+0x258/0x800
> [   81.836581]  cpu_startup_entry+0x26/0x30
> [   81.837002]  __pfx_ap_starting+0x0/0x10
> [   81.837444]  secondary_startup_64_no_verify+0x17a/0x17b
> [   81.837979]
> [   81.838166] Local variable nlbl_type.i created at:
> [   81.838596]  selinux_inet_conn_request+0xe3/0x4b0
> [   81.839078]  security_inet_conn_request+0xc0/0x160
> 
> KMSAN warning is reproducible with:
> * netlabel_mgmt_protocount is 0 (e.g. netlbl_enabled() returns 0)
> * CONFIG_SECURITY_NETWORK_XFRM may be set or not
> * CONFIG_KMSAN=y
> * `ssh USER@HOSTNAME /bin/date`
> 
> selinux_skb_peerlbl_sid() will call selinux_xfrm_skb_sid(), then fall
> to selinux_netlbl_skbuff_getsid() which will not initialize nlbl_type,
> but it will be passed to:
> 
>     err = security_net_peersid_resolve(nlbl_sid,
>                                        nlbl_type, xfrm_sid, sid);
> 
> and checked by KMSAN, although it will not be used inside
> security_net_peersid_resolve() (at least now), since this function
> will check either (xfrm_sid == SECSID_NULL) or (nlbl_sid ==
> SECSID_NULL) first and return before using uninitialized nlbl_type.
> 
> Signed-off-by: Andrew Kanner <andrew.kanner@xxxxxxxxx>
> Fixes: 220deb966ea5 ("SELinux: Better integration between peer labeling subsystems")
> ---
>  security/selinux/netlabel.c | 1 +
>  1 file changed, 1 insertion(+)

Thanks Andrew.  I'm going to drop the "Fixes" tag as the current code
isn't broken, as you mention in the commit description above, however,
I think this change is still worthwhile so I'm going to go ahead and
merge it into selinux/next.

--
paul-moore.com