From 9f30f83eb6347afa6b1d1df1065608c2b4485e2b Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 23 Aug 2016 13:59:33 -0700 Subject: [PATCH] udp: fix poll() issue with zero sized packets Laura tracked poll() [and friends] regression caused by commit e6afc8ace6dd ("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: e6afc8ace6dd ("udp: remove headers from UDP packets before queueing") Reported-by: Laura Abbott Signed-off-by: Eric Dumazet Tested-by: Laura Abbott --- net/ipv4/udp.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index e61f7cd..00d18c5 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1182,13 +1182,13 @@ out: * @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; -- 2.7.4