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udp: fix poll() issue with zero sized packets

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Laura tracked poll() [and friends] regression caused by commit
e6afc8ace6 ("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: e6afc8ace6 ("udp: remove headers from UDP packets before queueing")
Reported-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2016-08-23 13:59:33 -07:00 committed by David S. Miller
parent 28a10c426e
commit e83c6744e8
1 changed files with 6 additions and 6 deletions
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12
net/ipv4/udp.c
View file

@ -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;