Merge branch 'udp-peek'

Willem de Bruijn says:

====================
udp: support SO_PEEK_OFF

Support peeking at a non-zero offset for UDP sockets. Match the
existing behavior on Unix datagram sockets.

1/3 makes the sk_peek_offset functions safe to use outside locks
2/3 removes udp headers before enqueue, to simplify offset arithmetic
3/3 introduces SO_PEEK_OFFSET support, with Unix socket peek semantics.

Changes
  v1->v2
    - squash patches 3 and 4
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -2949,7 +2949,12 @@ int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
 				 struct iov_iter *from, int len);
 int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *frm);
 void skb_free_datagram(struct sock *sk, struct sk_buff *skb);
-void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb);
+void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len);
+static inline void skb_free_datagram_locked(struct sock *sk,
+					    struct sk_buff *skb)
+{
+	__skb_free_datagram_locked(sk, skb, 0);
+}
 int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags);
 int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len);
 int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len);

include/net/sock.h

@@ -457,28 +457,32 @@ struct sock {
 #define SK_CAN_REUSE	1
 #define SK_FORCE_REUSE	2
 
+int sk_set_peek_off(struct sock *sk, int val);
+
 static inline int sk_peek_offset(struct sock *sk, int flags)
 {
-	if ((flags & MSG_PEEK) && (sk->sk_peek_off >= 0))
-		return sk->sk_peek_off;
-	else
-		return 0;
+	if (unlikely(flags & MSG_PEEK)) {
+		s32 off = READ_ONCE(sk->sk_peek_off);
+		if (off >= 0)
+			return off;
+	}
+
+	return 0;
 }
 
 static inline void sk_peek_offset_bwd(struct sock *sk, int val)
 {
-	if (sk->sk_peek_off >= 0) {
-		if (sk->sk_peek_off >= val)
-			sk->sk_peek_off -= val;
-		else
-			sk->sk_peek_off = 0;
+	s32 off = READ_ONCE(sk->sk_peek_off);
+
+	if (unlikely(off >= 0)) {
+		off = max_t(s32, off - val, 0);
+		WRITE_ONCE(sk->sk_peek_off, off);
 	}
 }
 
 static inline void sk_peek_offset_fwd(struct sock *sk, int val)
 {
-	if (sk->sk_peek_off >= 0)
-		sk->sk_peek_off += val;
+	sk_peek_offset_bwd(sk, -val);
 }
 
 /*
@@ -1862,6 +1866,7 @@ void sk_reset_timer(struct sock *sk, struct timer_list *timer,
 
 void sk_stop_timer(struct sock *sk, struct timer_list *timer);
 
+int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
 int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
 
 int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb);

include/net/udp.h

@@ -158,6 +158,15 @@ static inline __sum16 udp_v4_check(int len, __be32 saddr,
 void udp_set_csum(bool nocheck, struct sk_buff *skb,
 		  __be32 saddr, __be32 daddr, int len);
 
+static inline void udp_csum_pull_header(struct sk_buff *skb)
+{
+	if (skb->ip_summed == CHECKSUM_NONE)
+		skb->csum = csum_partial(udp_hdr(skb), sizeof(struct udphdr),
+					 skb->csum);
+	skb_pull_rcsum(skb, sizeof(struct udphdr));
+	UDP_SKB_CB(skb)->cscov -= sizeof(struct udphdr);
+}
+
 struct sk_buff **udp_gro_receive(struct sk_buff **head, struct sk_buff *skb,
 				 struct udphdr *uh);
 int udp_gro_complete(struct sk_buff *skb, int nhoff);

net/core/datagram.c

@@ -301,16 +301,19 @@ void skb_free_datagram(struct sock *sk, struct sk_buff *skb)
 }
 EXPORT_SYMBOL(skb_free_datagram);
 
-void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb)
+void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len)
 {
 	bool slow;
 
 	if (likely(atomic_read(&skb->users) == 1))
 		smp_rmb();
-	else if (likely(!atomic_dec_and_test(&skb->users)))
+	else if (likely(!atomic_dec_and_test(&skb->users))) {
+		sk_peek_offset_bwd(sk, len);
 		return;
+	}
 
 	slow = lock_sock_fast(sk);
+	sk_peek_offset_bwd(sk, len);
 	skb_orphan(skb);
 	sk_mem_reclaim_partial(sk);
 	unlock_sock_fast(sk, slow);
@@ -318,7 +321,7 @@ void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb)
 	/* skb is now orphaned, can be freed outside of locked section */
 	__kfree_skb(skb);
 }
-EXPORT_SYMBOL(skb_free_datagram_locked);
+EXPORT_SYMBOL(__skb_free_datagram_locked);
 
 /**
  *	skb_kill_datagram - Free a datagram skbuff forcibly

net/core/sock.c

@@ -402,9 +402,8 @@ static void sock_disable_timestamp(struct sock *sk, unsigned long flags)
 }
 
 
-int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
+int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 {
-	int err;
 	unsigned long flags;
 	struct sk_buff_head *list = &sk->sk_receive_queue;
 
@@ -414,10 +413,6 @@ int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 		return -ENOMEM;
 	}
 
-	err = sk_filter(sk, skb);
-	if (err)
-		return err;
-
 	if (!sk_rmem_schedule(sk, skb, skb->truesize)) {
 		atomic_inc(&sk->sk_drops);
 		return -ENOBUFS;
@@ -440,6 +435,18 @@ int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 		sk->sk_data_ready(sk);
 	return 0;
 }
+EXPORT_SYMBOL(__sock_queue_rcv_skb);
+
+int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
+{
+	int err;
+
+	err = sk_filter(sk, skb);
+	if (err)
+		return err;
+
+	return __sock_queue_rcv_skb(sk, skb);
+}
 EXPORT_SYMBOL(sock_queue_rcv_skb);
 
 int sk_receive_skb(struct sock *sk, struct sk_buff *skb, const int nested)
@@ -2180,6 +2187,15 @@ void __sk_mem_reclaim(struct sock *sk, int amount)
 }
 EXPORT_SYMBOL(__sk_mem_reclaim);
 
+int sk_set_peek_off(struct sock *sk, int val)
+{
+	if (val < 0)
+		return -EINVAL;
+
+	sk->sk_peek_off = val;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(sk_set_peek_off);
 
 /*
  * Set of default routines for initialising struct proto_ops when

net/ipv4/af_inet.c

@@ -948,6 +948,7 @@ const struct proto_ops inet_dgram_ops = {
 	.recvmsg	   = inet_recvmsg,
 	.mmap		   = sock_no_mmap,
 	.sendpage	   = inet_sendpage,
+	.set_peek_off	   = sk_set_peek_off,
 #ifdef CONFIG_COMPAT
 	.compat_setsockopt = compat_sock_common_setsockopt,
 	.compat_getsockopt = compat_sock_common_getsockopt,

net/ipv4/udp.c

@@ -1294,7 +1294,7 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
 	DECLARE_SOCKADDR(struct sockaddr_in *, sin, msg->msg_name);
 	struct sk_buff *skb;
 	unsigned int ulen, copied;
-	int peeked, off = 0;
+	int peeked, peeking, off;
 	int err;
 	int is_udplite = IS_UDPLITE(sk);
 	bool checksum_valid = false;
@@ -1304,15 +1304,16 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
 		return ip_recv_error(sk, msg, len, addr_len);
 
 try_again:
+	peeking = off = sk_peek_offset(sk, flags);
 	skb = __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0),
 				  &peeked, &off, &err);
 	if (!skb)
-		goto out;
+		return err;
 
-	ulen = skb->len - sizeof(struct udphdr);
+	ulen = skb->len;
 	copied = len;
-	if (copied > ulen)
-		copied = ulen;
+	if (copied > ulen - off)
+		copied = ulen - off;
 	else if (copied < ulen)
 		msg->msg_flags |= MSG_TRUNC;
 
@@ -1322,18 +1323,16 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
 	 * coverage checksum (UDP-Lite), do it before the copy.
 	 */
 
-	if (copied < ulen || UDP_SKB_CB(skb)->partial_cov) {
+	if (copied < ulen || UDP_SKB_CB(skb)->partial_cov || peeking) {
 		checksum_valid = !udp_lib_checksum_complete(skb);
 		if (!checksum_valid)
 			goto csum_copy_err;
 	}
 
 	if (checksum_valid || skb_csum_unnecessary(skb))
-		err = skb_copy_datagram_msg(skb, sizeof(struct udphdr),
-					    msg, copied);
+		err = skb_copy_datagram_msg(skb, off, msg, copied);
 	else {
-		err = skb_copy_and_csum_datagram_msg(skb, sizeof(struct udphdr),
-						     msg);
+		err = skb_copy_and_csum_datagram_msg(skb, off, msg);
 
 		if (err == -EINVAL)
 			goto csum_copy_err;
@@ -1346,7 +1345,8 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
 			UDP_INC_STATS_USER(sock_net(sk),
 					   UDP_MIB_INERRORS, is_udplite);
 		}
-		goto out_free;
+		skb_free_datagram_locked(sk, skb);
+		return err;
 	}
 
 	if (!peeked)
@@ -1370,9 +1370,7 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
 	if (flags & MSG_TRUNC)
 		err = ulen;
 
-out_free:
-	skb_free_datagram_locked(sk, skb);
-out:
+	__skb_free_datagram_locked(sk, skb, peeking ? -err : err);
 	return err;
 
 csum_copy_err:
@@ -1500,7 +1498,7 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 		sk_incoming_cpu_update(sk);
 	}
 
-	rc = sock_queue_rcv_skb(sk, skb);
+	rc = __sock_queue_rcv_skb(sk, skb);
 	if (rc < 0) {
 		int is_udplite = IS_UDPLITE(sk);
 
@@ -1616,10 +1614,14 @@ int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 		}
 	}
 
-	if (rcu_access_pointer(sk->sk_filter) &&
-	    udp_lib_checksum_complete(skb))
-		goto csum_error;
+	if (rcu_access_pointer(sk->sk_filter)) {
+		if (udp_lib_checksum_complete(skb))
+			goto csum_error;
+		if (sk_filter(sk, skb))
+			goto drop;
+	}
 
+	udp_csum_pull_header(skb);
 	if (sk_rcvqueues_full(sk, sk->sk_rcvbuf)) {
 		UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_RCVBUFERRORS,
 				 is_udplite);

net/ipv6/af_inet6.c

@@ -561,6 +561,7 @@ const struct proto_ops inet6_dgram_ops = {
 	.recvmsg	   = inet_recvmsg,		/* ok		*/
 	.mmap		   = sock_no_mmap,
 	.sendpage	   = sock_no_sendpage,
+	.set_peek_off	   = sk_set_peek_off,
 #ifdef CONFIG_COMPAT
 	.compat_setsockopt = compat_sock_common_setsockopt,
 	.compat_getsockopt = compat_sock_common_getsockopt,

net/ipv6/udp.c

@@ -357,7 +357,7 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	struct inet_sock *inet = inet_sk(sk);
 	struct sk_buff *skb;
 	unsigned int ulen, copied;
-	int peeked, off = 0;
+	int peeked, peeking, off;
 	int err;
 	int is_udplite = IS_UDPLITE(sk);
 	bool checksum_valid = false;
@@ -371,15 +371,16 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		return ipv6_recv_rxpmtu(sk, msg, len, addr_len);
 
 try_again:
+	peeking = off = sk_peek_offset(sk, flags);
 	skb = __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0),
 				  &peeked, &off, &err);
 	if (!skb)
-		goto out;
+		return err;
 
-	ulen = skb->len - sizeof(struct udphdr);
+	ulen = skb->len;
 	copied = len;
-	if (copied > ulen)
-		copied = ulen;
+	if (copied > ulen - off)
+		copied = ulen - off;
 	else if (copied < ulen)
 		msg->msg_flags |= MSG_TRUNC;
 
@@ -391,17 +392,16 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	 * coverage checksum (UDP-Lite), do it before the copy.
 	 */
 
-	if (copied < ulen || UDP_SKB_CB(skb)->partial_cov) {
+	if (copied < ulen || UDP_SKB_CB(skb)->partial_cov || peeking) {
 		checksum_valid = !udp_lib_checksum_complete(skb);
 		if (!checksum_valid)
 			goto csum_copy_err;
 	}
 
 	if (checksum_valid || skb_csum_unnecessary(skb))
-		err = skb_copy_datagram_msg(skb, sizeof(struct udphdr),
-					    msg, copied);
+		err = skb_copy_datagram_msg(skb, off, msg, copied);
 	else {
-		err = skb_copy_and_csum_datagram_msg(skb, sizeof(struct udphdr), msg);
+		err = skb_copy_and_csum_datagram_msg(skb, off, msg);
 		if (err == -EINVAL)
 			goto csum_copy_err;
 	}
@@ -418,7 +418,8 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 						    UDP_MIB_INERRORS,
 						    is_udplite);
 		}
-		goto out_free;
+		skb_free_datagram_locked(sk, skb);
+		return err;
 	}
 	if (!peeked) {
 		if (is_udp4)
@@ -466,9 +467,7 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	if (flags & MSG_TRUNC)
 		err = ulen;
 
-out_free:
-	skb_free_datagram_locked(sk, skb);
-out:
+	__skb_free_datagram_locked(sk, skb, peeking ? -err : err);
 	return err;
 
 csum_copy_err:
@@ -554,7 +553,7 @@ static int __udpv6_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 		sk_incoming_cpu_update(sk);
 	}
 
-	rc = sock_queue_rcv_skb(sk, skb);
+	rc = __sock_queue_rcv_skb(sk, skb);
 	if (rc < 0) {
 		int is_udplite = IS_UDPLITE(sk);
 
@@ -648,8 +647,11 @@ int udpv6_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 	if (rcu_access_pointer(sk->sk_filter)) {
 		if (udp_lib_checksum_complete(skb))
 			goto csum_error;
+		if (sk_filter(sk, skb))
+			goto drop;
 	}
 
+	udp_csum_pull_header(skb);
 	if (sk_rcvqueues_full(sk, sk->sk_rcvbuf)) {
 		UDP6_INC_STATS_BH(sock_net(sk),
 				  UDP_MIB_RCVBUFERRORS, is_udplite);