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SubjectRe: [PATCH 3/3] Compare namespaces when comparing addresses in auth_unix cache.
Quoting Rob Landley (rlandley@parallels.com):
> On 04/08/2011 10:08 AM, Rob Landley wrote:
> > On 04/04/2011 10:46 PM, Serge E. Hallyn wrote:
> >> Does this need to take a reference? Or is there no way for an
> >> entry to outlive its netns? It sort of looks like
> >> svcauth_unix_info_release will ensure that doesn't happen, but
> >> I'm not convinced because other parts of the kernel can get
> >> to ip_map_init through the struct cache_detail.
> >
> > When I wrote this I thought the transport's get_net() and put_net()
> > would pin it, but after re-reading, the sunrpc code is disgustingly
> > convoluted enough that I can't easily reconstruct my earlier reasoning.
> > I'll add a get_net() and put_net() just to not have to worry about it.
>
> Ah-ha!
>
> Stanislav Kinsbursky helped me reconstruct some of the reasoning: we
> don't need to take a reference because we never actually dereference the
> struct net *, all we do is feed them to net_eq() which just compares the
> pointers for equality. (The inline function exists so it can compile to
> a constant "return 1" when configured out.)
>
> So if the network context did go away (which still shouldn't happen
> between the rpc_xprt and the struct nfs_client having references to it)
> we still wouldn't have a use-after-free problem because we're not
> looking at the memory, just the pointer.

Besides use-after-free, the other concern is an invalid net_eq()
result due to the * being re-used for a new netns. I assume that's
deemed "super-duper impossible" again bc of the rpc_xprt/nfs_client
references to it?

> So I shouldn't need to add get_net() and put_net() to the cache. Sound
> about right?

thanks,
-serge


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