Commit 627d2d6b authored by samanthakumar's avatar samanthakumar Committed by David S. Miller
Browse files

udp: enable MSG_PEEK at non-zero offset 



Enable peeking at UDP datagrams at the offset specified with socket
option SOL_SOCKET/SO_PEEK_OFF. Peek at any datagram in the queue, up
to the end of the given datagram.

Implement the SO_PEEK_OFF semantics introduced in commit ef64a54f
("sock: Introduce the SO_PEEK_OFF sock option"). Increase the offset
on peek, decrease it on regular reads.

When peeking, always checksum the packet immediately, to avoid
recomputation on subsequent peeks and final read.

The socket lock is not held for the duration of udp_recvmsg, so
peek and read operations can run concurrently. Only the last store
to sk_peek_off is preserved.

Signed-off-by: default avatarSam Kumar <samanthakumar@google.com>
Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e6afc8ac

include/linux/skbuff.h

+6 −1
Original line number Diff line number Diff line
@@ -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

+2 −0
Original line number Diff line number Diff line
@@ -457,6 +457,8 @@ 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 (unlikely(flags & MSG_PEEK)) {

net/core/datagram.c

+6 −3
Original line number Diff line number Diff line
@@ -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

+9 −0
Original line number Diff line number Diff line
@@ -2187,6 +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

+1 −0
Original line number Diff line number Diff line
@@ -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,

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