net/packet: convert po->origdev to an atomic flag

syzbot/KCAN reported that po->origdev can be read
while another thread is changing its value.

We can avoid this splat by converting this field
to an actual bit.

Following patches will convert remaining 1bit fields.

Fixes: 80feaacb ("[AF_PACKET]: Add option to return orig_dev to userspace.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -2184,7 +2184,7 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev,
 	sll = &PACKET_SKB_CB(skb)->sa.ll;
 	sll->sll_hatype = dev->type;
 	sll->sll_pkttype = skb->pkt_type;
-	if (unlikely(po->origdev))
+	if (unlikely(packet_sock_flag(po, PACKET_SOCK_ORIGDEV)))
 		sll->sll_ifindex = orig_dev->ifindex;
 	else
 		sll->sll_ifindex = dev->ifindex;
@@ -2461,7 +2461,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 	sll->sll_hatype = dev->type;
 	sll->sll_protocol = skb->protocol;
 	sll->sll_pkttype = skb->pkt_type;
-	if (unlikely(po->origdev))
+	if (unlikely(packet_sock_flag(po, PACKET_SOCK_ORIGDEV)))
 		sll->sll_ifindex = orig_dev->ifindex;
 	else
 		sll->sll_ifindex = dev->ifindex;
@@ -3914,9 +3914,7 @@ packet_setsockopt(struct socket *sock, int level, int optname, sockptr_t optval,
 		if (copy_from_sockptr(&val, optval, sizeof(val)))
 			return -EFAULT;
 
-		lock_sock(sk);
-		po->origdev = !!val;
-		release_sock(sk);
+		packet_sock_flag_set(po, PACKET_SOCK_ORIGDEV, val);
 		return 0;
 	}
 	case PACKET_VNET_HDR:
@@ -4065,7 +4063,7 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
 		val = po->auxdata;
 		break;
 	case PACKET_ORIGDEV:
-		val = po->origdev;
+		val = packet_sock_flag(po, PACKET_SOCK_ORIGDEV);
 		break;
 	case PACKET_VNET_HDR:
 		val = po->has_vnet_hdr;

net/packet/diag.c

@@ -25,7 +25,7 @@ static int pdiag_put_info(const struct packet_sock *po, struct sk_buff *nlskb)
 		pinfo.pdi_flags |= PDI_RUNNING;
 	if (po->auxdata)
 		pinfo.pdi_flags |= PDI_AUXDATA;
-	if (po->origdev)
+	if (packet_sock_flag(po, PACKET_SOCK_ORIGDEV))
 		pinfo.pdi_flags |= PDI_ORIGDEV;
 	if (po->has_vnet_hdr)
 		pinfo.pdi_flags |= PDI_VNETHDR;

net/packet/internal.h

@@ -116,9 +116,9 @@ struct packet_sock {
 	int			copy_thresh;
 	spinlock_t		bind_lock;
 	struct mutex		pg_vec_lock;
+	unsigned long		flags;
 	unsigned int		running;	/* bind_lock must be held */
 	unsigned int		auxdata:1,	/* writer must hold sock lock */
-				origdev:1,
 				has_vnet_hdr:1,
 				tp_loss:1,
 				tp_tx_has_off:1;
@@ -144,4 +144,24 @@ static inline struct packet_sock *pkt_sk(struct sock *sk)
 	return (struct packet_sock *)sk;
 }
 
+enum packet_sock_flags {
+	PACKET_SOCK_ORIGDEV,
+};
+
+static inline void packet_sock_flag_set(struct packet_sock *po,
+					enum packet_sock_flags flag,
+					bool val)
+{
+	if (val)
+		set_bit(flag, &po->flags);
+	else
+		clear_bit(flag, &po->flags);
+}
+
+static inline bool packet_sock_flag(const struct packet_sock *po,
+				    enum packet_sock_flags flag)
+{
+	return test_bit(flag, &po->flags);
+}
+
 #endif