nfc: hci: shdlc: Stop timers and work before freeing context

llc_shdlc_deinit() purges SHDLC skb queues and frees the llc_shdlc
structure while its timers and state machine work may still be active.

Timer callbacks can schedule sm_work, and sm_work accesses SHDLC state
and the skb queues. If teardown happens in parallel with a queued/running
work item, it can lead to UAF and other shutdown races.

Stop all SHDLC timers and cancel sm_work synchronously before purging the
queues and freeing the context.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 4a61cd6687fc ("NFC: Add an shdlc llc module to llc core")
Signed-off-by: Votokina Victoria <Victoria.Votokina@kaspersky.com>
Link: https://patch.msgid.link/20260203113158.2008723-1-Victoria.Votokina@kaspersky.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/nfc/hci/llc_shdlc.c b/net/nfc/hci/llc_shdlc.c
index 4fc37894860c9e65cf8531d9c66be1814119fcf6..08c8aa1530d8a09d9213aef326ca797372586053 100644 (file)
--- a/net/nfc/hci/llc_shdlc.c
+++ b/net/nfc/hci/llc_shdlc.c
@@ -762,6 +762,14 @@ static void llc_shdlc_deinit(struct nfc_llc *llc)
 {
        struct llc_shdlc *shdlc = nfc_llc_get_data(llc);
 
+       timer_shutdown_sync(&shdlc->connect_timer);
+       timer_shutdown_sync(&shdlc->t1_timer);
+       timer_shutdown_sync(&shdlc->t2_timer);
+       shdlc->t1_active = false;
+       shdlc->t2_active = false;
+
+       cancel_work_sync(&shdlc->sm_work);
+
        skb_queue_purge(&shdlc->rcv_q);
        skb_queue_purge(&shdlc->send_q);
        skb_queue_purge(&shdlc->ack_pending_q);