Re: Calling mnl_socket_sendto caused error of netlink attribute type 1 has an invalid length

[JH <jupiter.hce@gmail.com>]

Thanks Duncan, you are right, it was the wrong type and fixed.

Thank you and appreciate your helps.

Cheers.

- jh

On 12/31/19, Duncan Roe <duncan_roe@optusnet.com.au> wrote:
> 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.
>