On Mon, Dec 30, 2019 at 07:50:56PM +1100, JH wrote:
> Hi,
>
> I have following error of attribute type 1 has an invalid length when
> calling following mnl_socket_sendto(channel->mnlSocket, nlh,
> nlh->nlmsg_len), I cannot see what was wrong about it, the
> nlh->nlmsg_len = 40 which is from libnml, is that wrong? Please advise
> how to fix it.
>
> [ 3240.939609] netlink: 'wifi_signal': attribute type 1 has an invalid
> length. I have a WiFi function using nml API:
>
> typedef struct {
> struct mnl_socket *mnlSocket;
> char buf[BUFFER_SIZE];
> uint16_t channelId;
> uint32_t interfaceIndex;
> uint32_t sequence;
> void *context;
> } __attribute__ ((packed)) Netlink80211Channel_t;
>
> void WiFiScan::Send80211Message(struct nlmsghdr *nlh,
> Netlink80211Channel_t *channel) {
> if (mnl_socket_sendto(channel->mnlSocket, nlh, nlh->nlmsg_len) < 0) {
> std::cout << "Failed to send socket" << std::endl;
> }
> }
>
> Thank you.
>
> - jh
>
The kernel is complaining about the content of the message, rather than the
length. The message you send should consist of a header followed by a series of
attributes. Attributes are of the form <type> <length> <data>. <type> is always
uint8_t. The kernel has seen the an attribute of type 1 (NLA_U8) but the
following lenth byte was not 1 as it should have been. Quite possibly the
message is garbage.
The error message you see is output by function validate_nla() in file
lib/nlattr.c at line 178.
To get a more helpful answer, you would need to post a lot more code. Is it on
gitbub?
Cheers ... Duncan.
