Netlink header decoding

[Dmitry V. Levin]

Hi,

On Thu, May 05, 2016 at 10:04:51PM +0000, Fabien Siron wrote:
> Hi list,
> 
> I did a quick netlink header parser for sendmsg/recvmsg which does the
> following:
> 
> $ strace -qq -erecvmsg tests/netlink_inet_diag > /dev/null  
> recvmsg(1, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, \
> msg_iov(1)={len=96, type=20, flags=2, seq=0, pid=26615}, \
> msg_controllen=0, msg_flags=0}, 0) = 672
> 
> Of course, this is just a draft to get an idea on how the futur parser will
> work (so forget about the flags for the moment).
> Logically, the next step would be to handle the different protocols, but
> how can I obtain the protocol of a netlink socket fd?
> 
> I have two ideas:
> * keep all the pairs fd/protocol in a table when running the socket
> syscall.

sockets could be closed, cloned, and passed via SCM_RIGHTS messages.
Can you track it in a reliable way?

> * obtain the socket inode and then parse /proc/net/netlink to obtain the
> protocol.

As a modern alternative to /proc/net/netlink, you can use
NETLINK_SOCK_DIAG with AF_NETLINK sockets, too
(available in linux >= 3.10-rc1).


-- 
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