[nrf fromtree] bluetooth: mesh: pb_adv: ensure that bitwise NOT doesn't result in 0

Ensure that ~(link.rx.seg) & SEG_NVAL doesn't result in 0.

Fixes #84804
Coverity-CID: 393090

Signed-off-by: Pavel Vasilyev <[email protected]>
(cherry picked from commit fcf09dd)

Author: PavelVPV

subsys/bluetooth/mesh/pb_adv.c

@@ -637,7 +637,14 @@ static void gen_prov_start(struct prov_rx *rx, struct net_buf_simple *buf)
 
 	link.rx.last_seg = START_LAST_SEG(rx->gpc);
 
+	/* This (BIT(0) is set) can happen if we received a Transaction Continuation PDU, before
+	 * receiving a Transaction Start PDU (see `gen_prov_cont`). Now we received the Transaction
+	 * Start PDU and we can extract the last segment number. Knowing this, we check if
+	 * previously received segment exceeds the last segment number. If so, we reject the
+	 * Transaction Start PDU.
+	 */
 	if ((link.rx.seg & BIT(0)) &&
+	    ((link.rx.seg & SEG_NVAL) != SEG_NVAL) &&
 	    (find_msb_set((~link.rx.seg) & SEG_NVAL) - 1 > link.rx.last_seg)) {
 		LOG_ERR("Invalid segment index %u", seg);
 		prov_failed(PROV_ERR_NVAL_FMT);