| Message ID | 5d0f78b4-f850-4f73-dbb7-6c3d15d99c86@suse.cz |
|---|---|
| State | New |
| Headers | show |
On Mon, 2016-10-24 at 14:54 +0200, Jiri Slaby wrote: > Hello, > > as per man 7 udp: > In order to receive packets, the socket can be bound to > a local address first by using bind(2). Otherwise, > the socket layer will automatically assign a free local > port out of the range defined by /proc/sys/net/ipv4 > /ip_local_port_range and bind the socket to INADDR_ANY. > > I did not know that bind is unneeded, so I tried that. But it does not > work with this piece of code: > int main() > { > char buf[128]; > int fd = socket(AF_INET, SOCK_DGRAM, 0); > recv(fd, buf, sizeof(buf), 0); > } autobind makes little sense at recv() time really. How an application could expect to receive a frame to 'some socket' without even knowing its port ? How useful would that be exactly ? How TCP behaves ? I would say, fix the documentation if it is not correct.
On 10/24/2016, 03:03 PM, Eric Dumazet wrote: > On Mon, 2016-10-24 at 14:54 +0200, Jiri Slaby wrote: >> Hello, >> >> as per man 7 udp: >> In order to receive packets, the socket can be bound to >> a local address first by using bind(2). Otherwise, >> the socket layer will automatically assign a free local >> port out of the range defined by /proc/sys/net/ipv4 >> /ip_local_port_range and bind the socket to INADDR_ANY. >> >> I did not know that bind is unneeded, so I tried that. But it does not >> work with this piece of code: >> int main() >> { >> char buf[128]; >> int fd = socket(AF_INET, SOCK_DGRAM, 0); >> recv(fd, buf, sizeof(buf), 0); >> } > > autobind makes little sense at recv() time really. > > How an application could expect to receive a frame to 'some socket' > without even knowing its port ? For example struct sockaddr_storage sa; socklen_t slen = sizeof(sa); recv(fd, buf, sizeof(buf), MSG_DONTWAIT); getsockname(fd, (struct sockaddr *)&sa, &slen); recv(fd, buf, sizeof(buf), 0); works. > How useful would that be exactly ? No need for finding a free port and checking, for example. > How TCP behaves ? TCP is a completely different story. bind is documented to be required there. (And listen and accept.) > I would say, fix the documentation if it is not correct. I don't have a problem with either. I have only found, that the implementation differs from the documentation :). Is there some supervisor documentation (like POSIX) which should we be in conformance to? thanks, -- js suse labs
From 57c320998feb2e1e705a4ab6d3bbcb74c6ae65f0 Mon Sep 17 00:00:00 2001 From: Jiri Slaby <jslaby@suse.cz> Date: Sat, 22 Oct 2016 12:10:53 +0200 Subject: [PATCH] net: autobind UDP on recv Signed-off-by: Jiri Slaby <jslaby@suse.cz> --- include/net/inet_common.h | 1 + net/ipv4/af_inet.c | 3 ++- net/ipv4/udp.c | 5 +++++ net/ipv6/udp.c | 5 +++++ 4 files changed, 13 insertions(+), 1 deletion(-) diff --git a/include/net/inet_common.h b/include/net/inet_common.h index 5d683428fced..ba224ed3dd36 100644 --- a/include/net/inet_common.h +++ b/include/net/inet_common.h @@ -27,6 +27,7 @@ ssize_t inet_sendpage(struct socket *sock, struct page *page, int offset, int inet_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, int flags); int inet_shutdown(struct socket *sock, int how); +int inet_autobind(struct sock *sk); int inet_listen(struct socket *sock, int backlog); void inet_sock_destruct(struct sock *sk); int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len); diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c index 9648c97e541f..d23acb11cdb0 100644 --- a/net/ipv4/af_inet.c +++ b/net/ipv4/af_inet.c @@ -171,7 +171,7 @@ EXPORT_SYMBOL(inet_sock_destruct); * Automatically bind an unbound socket. */ -static int inet_autobind(struct sock *sk) +int inet_autobind(struct sock *sk) { struct inet_sock *inet; /* We may need to bind the socket. */ @@ -187,6 +187,7 @@ static int inet_autobind(struct sock *sk) release_sock(sk); return 0; } +EXPORT_SYMBOL_GPL(inet_autobind); /* * Move a socket into listening state. diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 82fb78265f4b..ceb07c83af17 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1360,6 +1360,11 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock, if (flags & MSG_ERRQUEUE) return ip_recv_error(sk, msg, len, addr_len); + /* We may need to bind the socket. */ + if (!inet_sk(sk)->inet_num && !sk->sk_prot->no_autobind && + inet_autobind(sk)) + return -EAGAIN; + try_again: peeking = off = sk_peek_offset(sk, flags); skb = __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0), diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c index 71963b23d5a5..1c3dafc3d91e 100644 --- a/net/ipv6/udp.c +++ b/net/ipv6/udp.c @@ -341,6 +341,11 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, if (np->rxpmtu && np->rxopt.bits.rxpmtu) return ipv6_recv_rxpmtu(sk, msg, len, addr_len); + /* We may need to bind the socket. */ + if (!inet_sk(sk)->inet_num && !sk->sk_prot->no_autobind && + inet_autobind(sk)) + return -EAGAIN; + try_again: peeking = off = sk_peek_offset(sk, flags); skb = __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0), -- 2.10.1
Hello, as per man 7 udp: In order to receive packets, the socket can be bound to a local address first by using bind(2). Otherwise, the socket layer will automatically assign a free local port out of the range defined by /proc/sys/net/ipv4 /ip_local_port_range and bind the socket to INADDR_ANY. I did not know that bind is unneeded, so I tried that. But it does not work with this piece of code: int main() { char buf[128]; int fd = socket(AF_INET, SOCK_DGRAM, 0); recv(fd, buf, sizeof(buf), 0); } The recv above never returns (even if I bomb all ports from the range). ss -ulpan is silent too. As a workaround, I can stick a dummy write/send before recv: write(fd, "", 0); And it starts working. ss suddenly displays a port which the program listens on. I think the UDP recv path should do inet_autobind as I have done in the attached patch. But my knowledge is very limited in that area, so I have no idea whether that is correct at all. thanks, -- js suse labs