Re: [PATCH] netlink: fix for too early rmmod

[David Miller <davem@davemloft.net>]

From: Patrick McHardy <kaber@trash.net>
Date: Tue, 02 Feb 2010 15:55:25 +0100

> Alexey Dobriyan wrote:
>> Netlink code does module autoload if protocol userspace is asking for is
>> not ready. However, module can dissapear right after it was autoloaded.
>> Example: modprobe/rmmod stress-testing and xfrm_user.ko providing NETLINK_XFRM.
>> 
>> netlink_create() in such situation _will_ create userspace socket and
>> _will_not_ pin module. Now if module was removed and we're going to call
>> ->netlink_rcv into nothing:
>> 
>> BUG: unable to handle kernel paging request at ffffffffa02f842a
>> 					       ^^^^^^^^^^^^^^^^
>> 	modules are loaded near these addresses here
>> 
>> ...
>> 
>> If module was quickly removed after autoloading, return -E.
>> 
>> Return -EPROTONOSUPPORT if module was quickly removed after autoloading.
>> 
>> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
>> ---
>> 
>> 	NOTE: due to commit 513c25000005257e5474f261bf27d4a3c1dff1e3
>> 	"[NETLINK]: Don't prevent creating sockets when no kernel socket is registered"
>> 	error should probably be -ENOENT, but I have no idea what this
>> 	pam-audit thing is.
> 
> Quoting from the thread back then (couldn't find a public reference):
> 
>> FC4 includes a pam-0.77-audit.patch which adds a pam module that
>> uses libaudit to probe for audit availability. It calls audit_open
>> and ignores connection refused but returns an pam error for all
>> other errors.
> 
> The current version of libaudit properly checks for EPROTONOSUPPORT,
> but I don't know when this was fixed and whether we can assume the
> broken code is not used anymore.

In any event, the EPROTONOSUPPORT is being returned now in a case
that has been OOPS'ing.  So I think it's safe to apply Alexey's
fix as-is, and that is what I have just done in net-2.6 :-)

Thanks!