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sockets: update SOCKET_ADDRESS_TYPE_FD listen(2) backlog 

socket_get_fd() fails with the error "socket_get_fd: too many
connections" if the given listen backlog value is not 1.

Not all callers set the backlog to 1. For example, commit
582d4210eb ("qemu-nbd: Use SOMAXCONN for
socket listen() backlog") uses SOMAXCONN. This will always fail with in
socket_get_fd().

This patch calls listen(2) on the fd to update the backlog value. The
socket may already be in the listen state. I have tested that this works
on Linux 5.10 and macOS Catalina.

As a bonus this allows us to detect when the fd cannot listen. Now we'll
be able to catch unbound or connected fds in socket_listen().

Drop the num argument from socket_get_fd() since this function is also
called by socket_connect() where a listen backlog value does not make
sense.

Fixes: e5b6353cf2 ("socket: Add backlog parameter to socket_listen")
Reported-by: Richard W.M. Jones <rjones@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20210310173004.420190-1-stefanha@redhat.com>
Tested-by: Richard W.M. Jones <rjones@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2021-03-10 17:30:04 +00:00 committed by Eric Blake
parent f9a576a818
commit 37179e9ea4
1 changed files with 22 additions and 7 deletions
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29
util/qemu-sockets.c
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@ -1116,14 +1116,10 @@ fail:
return NULL;
}
static int socket_get_fd(const char *fdstr, int num, Error **errp)
static int socket_get_fd(const char *fdstr, Error **errp)
{
Monitor *cur_mon = monitor_cur();
int fd;
if (num != 1) {
error_setg_errno(errp, EINVAL, "socket_get_fd: too many connections");
return -1;
}
if (cur_mon) {
fd = monitor_get_fd(cur_mon, fdstr, errp);
if (fd < 0) {
@ -1159,7 +1155,7 @@ int socket_connect(SocketAddress *addr, Error **errp)
break;
case SOCKET_ADDRESS_TYPE_FD:
fd = socket_get_fd(addr->u.fd.str, 1, errp);
fd = socket_get_fd(addr->u.fd.str, errp);
break;
case SOCKET_ADDRESS_TYPE_VSOCK:
@ -1187,7 +1183,26 @@ int socket_listen(SocketAddress *addr, int num, Error **errp)
break;
case SOCKET_ADDRESS_TYPE_FD:
fd = socket_get_fd(addr->u.fd.str, num, errp);
fd = socket_get_fd(addr->u.fd.str, errp);
if (fd < 0) {
return -1;
}
/*
* If the socket is not yet in the listen state, then transition it to
* the listen state now.
*
* If it's already listening then this updates the backlog value as
* requested.
*
* If this socket cannot listen because it's already in another state
* (e.g. unbound or connected) then we'll catch the error here.
*/
if (listen(fd, num) != 0) {
error_setg_errno(errp, errno, "Failed to listen on fd socket");
closesocket(fd);
return -1;
}
break;
case SOCKET_ADDRESS_TYPE_VSOCK: