On Fri, Jun 4, 2021 at 2:54 AM Christian Brauner christian.brauner@ubuntu.com wrote:
On Thu, Jun 03, 2021 at 03:52:29PM -0700, Cong Wang wrote:
On Wed, Jun 2, 2021 at 2:14 AM Christian Brauner christian.brauner@ubuntu.com wrote:
But the point is that ns->ops should never be accessed when that namespace type is disabled. Or in other words, the bug is that something in netns makes use of namespace features when they are disabled. If we handle ->ops being NULL we might be tapering over a real bug somewhere.
It is merely a protocol between fs/nsfs.c and other namespace users, so there is certainly no right or wrong here, the only question is which one is better.
Jakub's proposal in the other mail makes sense and falls in line with how the rest of the netns getters are implemented. For example get_net_ns_fd_fd():
It does not make any sense to me. get_net_ns() merely increases the netns refcount, which is certainly fine for init_net too, no matter CONFIG_NET_NS is enabled or disabled. Returning EOPNOTSUPP there is literally saying we do not support increasing init_net refcount, which is of course false.
struct net *get_net_ns_by_fd(int fd) { return ERR_PTR(-EINVAL); }
There is a huge difference between just increasing netns refcount and retrieving it by fd, right? I have no idea why you bring this up, calling them getters is missing their difference.
This argument doesn't hold up. All netns helpers ultimately increase the reference count of the net namespace they find. And if any of them perform operations where they are called in environments wherey they need CONFIG_NET_NS they handle this case at compile time.
Let me explain it in this more straight way: what is the protocol here for indication of !CONFIG_XXX_NS? Clearly it must be ns->ops==NULL, because all namespaces use the following similar pattern:
#ifdef CONFIG_NET_NS net->ns.ops = &netns_operations; #endif
Now you are arguing the protocol is not this, but it is the getter of open_related_ns() returns an error pointer.
(Pluse they are defined in a central place in net/net_namespace.{c,h}. That includes the low-level get_net() function and all the others. get_net_ns() is the only one that's defined out of band. So get_net_ns() currently is arguably also misplaced.)
Of course they do, only struct ns_common is generic. What's your point? Each ns.ops is defined by each namespace too.
The problem I have with fixing this in nsfs is that it gives the impression that this is a bug in nsfs whereas it isn't and it potentially helps tapering over other bugs.
Like I keep saying, this is just a protocol, there is no right or wrong here. If the protocol is just ops==NULL, then there is nothing wrong use it.
(BTW, we have a lot of places that use ops==NULL as a protocol, they work really well.)
get_net_ns() is only called for codepaths that call into nsfs via open_related_ns() and it's the only namespace that does this. But
I am pretty sure userns does the same:
197 case NS_GET_USERNS: 198 return open_related_ns(ns, ns_get_owner);
open_related_ns() is only well defined if CONFIG_<NAMESPACE_TYPE> is set. For example, none of the procfs namespace f_ops will be set for !CONFIG_NET_NS. So clearly the socket specific getter here is buggy as it doesn't account for !CONFIG_NET_NS and it should be fixed.
If the protocol is just ops==NULL, then the core part should just check ops==NULL. Pure and simple. I have no idea why you do not admit the fact that every namespace intentionally leaves ops as NULL when its config is disabled.
Plus your fix leaks references to init netns without fixing get_net_ns() too.
I thought it is 100% clear that this patch is not from me?
Plus, the PoC patch from me actually suggests to change open_related_ns(), not __ns_get_path(). I have no idea why you both miss it.
Thanks.