Re: [nft PATCH RFC] monitor: Support printing processes which caused the event

[Phil Sutter <phil@nwl.cc>]

Hi,

On Wed, May 10, 2017 at 01:57:48PM +0200, Florian Westphal wrote:
> Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > On Wed, May 10, 2017 at 01:27:24PM +0200, Florian Westphal wrote:
> > > While most programs set it to their process id there is no guarantee.
> > > Its just a (unique) 32 bit identifier.
> > 
> > It's actually the kernel that decides what portID the socket gets
> > IIRC. For the first socket it uses the process ID, then for follow up
> > sockets, it just looks for a spare ID in the negative range of the 32
> > bit, if my memory serves well.
> 
> Argh, yes, of course...
> 
> > > Afaics one has to use /proc/net/netlink to map the portid to the inode
> > > and then walk /proc/*/fd/* to find the socket with that inode.
> > > 
> > > Perhaps there is a simpler way, maybe you can check what ss is doing
> > > and what info can be obtained via netlink diag.
> > 
> > I wouldn't be surprise if we need more kernel infrastructure to deal
> > with this. Parsing /proc for a netlink thing is definitely not ideal.
> 
> Yes.  From nft monitor point of view the most easy solution would be
> if the process id (or even the name?) would be sent back to userspace in a netlink
> attribute.  Do you think we can extend nf_tables to include
> get_task_comm() name and/or pid when/if we send update notifications?
> 
> (The pid is actually not that useful as process might have exited
> already).

The question is where to put it. Looking at the netlink message
structure, I see two options:

A) Extend struct nfgenmsg to contain PID and process name (a buffer of
   length TASK_COMM_LEN).
B) Add type-specific attributes for each type, like NFTA_RULE_PID and
   NFTA_RULE_PNAME.

The problem with A) is that it will break older user space expecting
sizeof(struct nfgenmsg) to be shorter. Additional attributes should not
be a problem here, but having to add them for each object type seems to
be a really ugly solution.

Cheers, Phil