svn commit: r323873 - head/sys/netgraph

[Eugene Grosbein]

On 26.09.2017 03:59, Gleb Smirnoff wrote:
> On Thu, Sep 21, 2017 at 08:16:11PM +0000, Eugene Grosbein wrote:
> E> Author: eugen (ports committer)
> E> Date: Thu Sep 21 20:16:10 2017
> E> New Revision: 323873
> E> URL: https://svnweb.freebsd.org/changeset/base/323873
> E> 
> E> Log:
> E>   Unprotected modification of ng_iface(4) private data leads to kernel panic.
> E>   Fix a race with per-node read-mostly lock and refcounting for a hook.
> 
> The patch is far from ideal. Netgraph already has internal locking,
> which guarantess write semantics for "disconnect" and "newhook"
> scenarios. As well as read semantics for "rcvdata".
> 
> Since ng_iface is a gate node, that gates data between netgraph and the
> big network stack, it of course needs extra locking in the interface
> output method. But better piggyback on the netgraph locking, rather than
> add your own, IMHO.

I'm afraid you have not read the change well enough.
It does utilizes generic netgraph locking like NG_HOOK_REF(hook)
for entities visible to base netgraph code.

And it uses own locking only to protect private ng_iface structures
from parallel modifications with another kernel thread runnning same
ng_iface code. It uses lightweight rmlock there as that is network hot path
and anyway, other netgraph code has nothing to do with node's private data.