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Commit e83c6744 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

udp: fix poll() issue with zero sized packets 



Laura tracked poll() [and friends] regression caused by commit
e6afc8ac ("udp: remove headers from UDP packets before queueing")

udp_poll() needs to know if there is a valid packet in receive queue,
even if its payload length is 0.

Change first_packet_length() to return an signed int, and use -1
as the indication of an empty queue.

Fixes: e6afc8ac ("udp: remove headers from UDP packets before queueing")
Reported-by: default avatarLaura Abbott <labbott@redhat.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Tested-by: default avatarLaura Abbott <labbott@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 28a10c42

net/ipv4/udp.c

+6 −6
Original line number Diff line number Diff line
@@ -1182,13 +1182,13 @@ int udp_sendpage(struct sock *sk, struct page *page, int offset, 
 *	@sk: socket

 *

 *	Drops all bad checksum frames, until a valid one is found.

 *	Returns the length of found skb, or 0 if none is found.

 *	Returns the length of found skb, or -1 if none is found.

 */

static unsigned int first_packet_length(struct sock *sk)

static int first_packet_length(struct sock *sk)

{

	struct sk_buff_head list_kill, *rcvq = &sk->sk_receive_queue;

	struct sk_buff *skb;

	unsigned int res;

	int res;



	__skb_queue_head_init(&list_kill);
@@ -1203,7 +1203,7 @@ static unsigned int first_packet_length(struct sock *sk) 
		__skb_unlink(skb, rcvq);

		__skb_queue_tail(&list_kill, skb);

	}

	res = skb ? skb->len : 0;

	res = skb ? skb->len : -1;

	spin_unlock_bh(&rcvq->lock);



	if (!skb_queue_empty(&list_kill)) {
@@ -1232,7 +1232,7 @@ int udp_ioctl(struct sock *sk, int cmd, unsigned long arg) 


	case SIOCINQ:

	{

		unsigned int amount = first_packet_length(sk);

		int amount = max_t(int, 0, first_packet_length(sk));



		return put_user(amount, (int __user *)arg);

	}
@@ -2184,7 +2184,7 @@ unsigned int udp_poll(struct file *file, struct socket *sock, poll_table *wait) 


	/* Check for false positives due to checksum errors */

	if ((mask & POLLRDNORM) && !(file->f_flags & O_NONBLOCK) &&

	    !(sk->sk_shutdown & RCV_SHUTDOWN) && !first_packet_length(sk))

	    !(sk->sk_shutdown & RCV_SHUTDOWN) && first_packet_length(sk) == -1)

		mask &= ~(POLLIN | POLLRDNORM);



	return mask;