Re: [Qemu-devel] [PATCH] linux-user: manage SOCK_PACKET socket type.

[Laurent Vivier <laurent@vivier.eu>]

Le 27/10/2015 12:50, Peter Maydell a écrit :
> On 27 October 2015 at 03:09, Laurent Vivier <laurent@vivier.eu> wrote:
>> Le 26/10/2015 15:40, Peter Maydell a écrit :
>>> This confuses me. The packet(7) manpage suggests there are two flavours
>>> of packet socket:
>>>  (1) legacy AF_INET + SOCK_PACKET
>>>  (2) new style AF_PACKET + SOCK_RAW / SOCK_DGRAM
>>>
>>> but this comment suggests it's trying to handle AF_PACKET + SOCK_PACKET ?
>>
>> In fact, I've started not from the man page, but from a non working dhcp
>> client, originally with a m68k target and etch-m68k distro, and I've met
>> again this problem on a ppc target and jessie distro.
> 
>> kernel 4.3.0-rc3, net/packet/af_packet.c:
>>
>>    2961
>>    2962 static int packet_bind_spkt(struct socket *sock, struct sockaddr
>> *uaddr,
>>    2963                             int addr_len)
>>    2964 {
>>    2965         struct sock *sk = sock->sk;
>>    2966         char name[15];
>>    2967         struct net_device *dev;
>>    2968         int err = -ENODEV;
>>    2969
>>    2970         /*
>>    2971          *      Check legality
>>    2972          */
>>    2973
>>    2974         if (addr_len != sizeof(struct sockaddr))
>>    2975                 return -EINVAL;
>>    2976         strlcpy(name, uaddr->sa_data, sizeof(name));
>>    2977
>>    2978         dev = dev_get_by_name(sock_net(sk), name);
>>    2979         if (dev)
>>    2980                 err = packet_do_bind(sk, dev, pkt_sk(sk)->num);
>>    2981         return err;
>>    2982 }
>> ...
>>    4246 static const struct proto_ops packet_ops_spkt = {
>>    4247         .family =       PF_PACKET,
>> ...
>>    4250         .bind =         packet_bind_spkt,
>> ...
>>    3022
>>    3023 static int packet_create(struct net *net, struct socket *sock,
>> int protocol,
>>    3024                          int kern)
>> ...
>>    3045         if (sock->type == SOCK_PACKET)
>>    3046                 sock->ops = &packet_ops_spkt;
>> ...
> 
> Yes, but also:
> http://lxr.free-electrons.com/source/net/socket.c#L1109
> 
> 1114         if (family == PF_INET && type == SOCK_PACKET) {
> 1115                 static int warned;
> 1116                 if (!warned) {
> 1117                         warned = 1;
> 1118                         pr_info("%s uses obsolete (PF_INET,SOCK_PACKET)\n",
> 1119                                 current->comm);
> 1120                 }
> 1121                 family = PF_PACKET;
> 1122         }
> 
> So I think my conclusion is:
>  * Original 2.0 kernels used PF_INET + SOCK_PACKET
>  * When the non-legacy stuff was added and this compat warning
>    came in, the (accidental?) result was that PF_PACKET + SOCK_PACKET
>    gave a warning, PF_PACKET + SOCK_PACKET gave legacy behaviour
>    without a warning, and PF_PACKET + SOCK_RAW/SOCK_DGRAM gave
>    the new interface
>  * Some userspace programs responded not by updating to the new
>    non-legacy interface, but by moving to PF_PACKET + SOCK_PACKET
>    which just suppresses the warning
> 
> So we should special case both PF_INET + SOCK_PACKET and
> PF_PACKET + SOCK_PACKET (but not any other PF_* + SOCK_PACKET).

I'll try that too...

Laurent