netdev-linux: Don't close(0) when closing an ordinary netdev.

Calling close(0) at random points is bad.  It means that the next call to
socket() or open() returns fd 0.  Then the next time a netdev gets closed,
that socket or file fd gets closed too, and you end up with weird "Bad
file descriptor" errors.

Found by installing the following as lib/unistd.h in the source tree:

#ifndef UNISTD_H
#define UNISTD_H 1

#include <stdlib.h>
#include_next <unistd.h>

#undef close
#define close(fd) rpl_close(fd)

static inline int rpl_close(int fd)
{
    if (!fd) {
        abort();
    }
    return (close)(fd);
}

#endif

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/netdev-linux.c b/lib/netdev-linux.c
index 4f6b20b27..d45349b29 100644
--- a/lib/netdev-linux.c
+++ b/lib/netdev-linux.c
@@ -821,7 +821,6 @@ netdev_linux_open(struct netdev_dev *netdev_dev_, int ethertype,
 
     if (!strcmp(netdev_dev_get_type(netdev_dev_), "tap")) {
         netdev->fd = netdev_dev->state.tap.fd;
-
     } else if (ethertype != NETDEV_ETH_TYPE_NONE) {
         struct sockaddr_ll sll;
         int protocol;
@@ -869,6 +868,8 @@ netdev_linux_open(struct netdev_dev *netdev_dev_, int ethertype,
         if (error) {
             goto error;
         }
+    } else {
+        netdev->fd = -1;
     }
 
     *netdevp = &netdev->netdev;