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

[Andrew Kanner <andrew.kanner@gmail.com>]

On Tue, Aug 15, 2023 at 11:11:57PM +0200, Greg KH wrote:
> On Tue, Aug 15, 2023 at 10:59:17PM +0200, Andrew Kanner 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@gmail.com>
> > ---
> >  security/selinux/netlabel.c | 1 +
> >  1 file changed, 1 insertion(+)
> 
> What git commit id does this fix?  Does it also need to go to older
> kernels?  If so, how far back?
> 
> thanks,
> 
> greg k-h

Thanks, Greg. I mentioned it in the cover letter only because I'm not
sure, it seems to be:

Fixes: 220deb966ea5 ("SELinux: Better integration between peer labeling subsystems")

which is ~v2.6.24, I believe. I wish I could use KMSAN there -)

But I checked - this uninit var will not be used on 220deb966ea5 and
the function will return earlier as well. As far as I see this is just
a KMSAN warning for the uninitialized function argument.

PS: maybe we should check if KMSAN is be able to check the possible
usage of such uninit arguments.

-- 
Andrew Kanner