udplite: fix various data-races

udp->pcflag, udp->pcslen and udp->pcrlen reads/writes are racy.

Move udp->pcflag to udp->udp_flags for atomicity,
and add READ_ONCE()/WRITE_ONCE() annotations for pcslen and pcrlen.

Fixes: ba4e58eca8aa ("[NET]: Supporting UDP-Lite (RFC 3828) in Linux")
Signed-off-by: Eric Dumazet <[e-mail]>
Reviewed-by: Willem de Bruijn <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

include/linux/udp.h

···
 	UDP_FLAGS_ACCEPT_FRAGLIST,
 	UDP_FLAGS_ACCEPT_L4,
 	UDP_FLAGS_ENCAP_ENABLED, /* This socket enabled encap */
+	UDP_FLAGS_UDPLITE_SEND_CC, /* set via udplite setsockopt */
+	UDP_FLAGS_UDPLITE_RECV_CC, /* set via udplite setsockopt */
 };
 
 struct udp_sock {
···
 	int		 pending;	/* Any pending frames ? */
 	__u8		 encap_type;	/* Is this an Encapsulation socket? */
 
-/* indicator bits used by pcflag: */
-#define UDPLITE_SEND_CC  0x1  		/* set via udplite setsockopt         */
-#define UDPLITE_RECV_CC  0x2		/* set via udplite setsocktopt        */
-	__u8		 pcflag;        /* marks socket as UDP-Lite if > 0    */
 	/*
 	 * Following member retains the information to create a UDP header
 	 * when the socket is uncorked.

include/net/udplite.h

···
 /* Fast-path computation of checksum. Socket may not be locked. */
 static inline __wsum udplite_csum(struct sk_buff *skb)
 {
-	const struct udp_sock *up = udp_sk(skb->sk);
 	const int off = skb_transport_offset(skb);
+	const struct sock *sk = skb->sk;
 	int len = skb->len - off;
 
-	if ((up->pcflag & UDPLITE_SEND_CC) && up->pcslen < len) {
-		if (0 < up->pcslen)
-			len = up->pcslen;
-		udp_hdr(skb)->len = htons(up->pcslen);
+	if (udp_test_bit(UDPLITE_SEND_CC, sk)) {
+		u16 pcslen = READ_ONCE(udp_sk(sk)->pcslen);
+
+		if (pcslen < len) {
+			if (pcslen > 0)
+				len = pcslen;
+			udp_hdr(skb)->len = htons(pcslen);
+		}
 	}
 	skb->ip_summed = CHECKSUM_NONE;     /* no HW support for checksumming */
 

net/ipv4/udp.c

···
 	/*
 	 * 	UDP-Lite specific tests, ignored on UDP sockets
 	 */
-	if ((up->pcflag & UDPLITE_RECV_CC)  &&  UDP_SKB_CB(skb)->partial_cov) {
+	if (udp_test_bit(UDPLITE_RECV_CC, sk) && UDP_SKB_CB(skb)->partial_cov) {
+		u16 pcrlen = READ_ONCE(up->pcrlen);
 
 		/*
 		 * MIB statistics other than incrementing the error count are
···
 		 * delivery of packets with coverage values less than a value
 		 * provided by the application."
 		 */
-		if (up->pcrlen == 0) {          /* full coverage was set  */
+		if (pcrlen == 0) {          /* full coverage was set  */
 			net_dbg_ratelimited("UDPLite: partial coverage %d while full coverage %d requested\n",
 					    UDP_SKB_CB(skb)->cscov, skb->len);
 			goto drop;
···
 		 * that it wants x while sender emits packets of smaller size y.
 		 * Therefore the above ...()->partial_cov statement is essential.
 		 */
-		if (UDP_SKB_CB(skb)->cscov  <  up->pcrlen) {
+		if (UDP_SKB_CB(skb)->cscov < pcrlen) {
 			net_dbg_ratelimited("UDPLite: coverage %d too small, need min %d\n",
-					    UDP_SKB_CB(skb)->cscov, up->pcrlen);
+					    UDP_SKB_CB(skb)->cscov, pcrlen);
 			goto drop;
 		}
 	}
···
 			val = 8;
 		else if (val > USHRT_MAX)
 			val = USHRT_MAX;
-		up->pcslen = val;
-		up->pcflag |= UDPLITE_SEND_CC;
+		WRITE_ONCE(up->pcslen, val);
+		udp_set_bit(UDPLITE_SEND_CC, sk);
 		break;
 
 	/* The receiver specifies a minimum checksum coverage value. To make
···
 			val = 8;
 		else if (val > USHRT_MAX)
 			val = USHRT_MAX;
-		up->pcrlen = val;
-		up->pcflag |= UDPLITE_RECV_CC;
+		WRITE_ONCE(up->pcrlen, val);
+		udp_set_bit(UDPLITE_RECV_CC, sk);
 		break;
 
 	default:
···
 	/* The following two cannot be changed on UDP sockets, the return is
 	 * always 0 (which corresponds to the full checksum coverage of UDP). */
 	case UDPLITE_SEND_CSCOV:
-		val = up->pcslen;
+		val = READ_ONCE(up->pcslen);
 		break;
 
 	case UDPLITE_RECV_CSCOV:
-		val = up->pcrlen;
+		val = READ_ONCE(up->pcrlen);
 		break;
 
 	default:

net/ipv6/udp.c

···
 	/*
 	 * UDP-Lite specific tests, ignored on UDP sockets (see net/ipv4/udp.c).
 	 */
-	if ((up->pcflag & UDPLITE_RECV_CC)  &&  UDP_SKB_CB(skb)->partial_cov) {
+	if (udp_test_bit(UDPLITE_RECV_CC, sk) && UDP_SKB_CB(skb)->partial_cov) {
+		u16 pcrlen = READ_ONCE(up->pcrlen);
 
-		if (up->pcrlen == 0) {          /* full coverage was set  */
+		if (pcrlen == 0) {          /* full coverage was set  */
 			net_dbg_ratelimited("UDPLITE6: partial coverage %d while full coverage %d requested\n",
 					    UDP_SKB_CB(skb)->cscov, skb->len);
 			goto drop;
 		}
-		if (UDP_SKB_CB(skb)->cscov  <  up->pcrlen) {
+		if (UDP_SKB_CB(skb)->cscov < pcrlen) {
 			net_dbg_ratelimited("UDPLITE6: coverage %d too small, need min %d\n",
-					    UDP_SKB_CB(skb)->cscov, up->pcrlen);
+					    UDP_SKB_CB(skb)->cscov, pcrlen);
 			goto drop;
 		}
 	}