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[ Upstream commit18a110b022] Curtis Taylor and Jon Maxwell reported and debugged a crash on 3.10 based kernel. Crash occurs in ctnetlink_conntrack_events because net->nfnl socket is NULL. The nfnl socket was set to NULL by netns destruction running on another cpu. The exiting network namespace calls the relevant destructors in the following order: 1. ctnetlink_net_exit_batch This nulls out the event callback pointer in struct netns. 2. nfnetlink_net_exit_batch This nulls net->nfnl socket and frees it. 3. nf_conntrack_cleanup_net_list This removes all remaining conntrack entries. This is order is correct. The only explanation for the crash so ar is: cpu1: conntrack is dying, eviction occurs: -> nf_ct_delete() -> nf_conntrack_event_report \ -> nf_conntrack_eventmask_report -> notify->fcn() (== ctnetlink_conntrack_events). cpu1: a. fetches rcu protected pointer to obtain ctnetlink event callback. b. gets interrupted. cpu2: runs netns exit handlers: a runs ctnetlink destructor, event cb pointer set to NULL. b runs nfnetlink destructor, nfnl socket is closed and set to NULL. cpu1: c. resumes and trips over NULL net->nfnl. Problem appears to be that ctnetlink_net_exit_batch only prevents future callers of nf_conntrack_eventmask_report() from obtaining the callback. It doesn't wait of other cpus that might have already obtained the callbacks address. I don't see anything in upstream kernels that would prevent similar crash: We need to wait for all cpus to have exited the event callback. Fixes:9592a5c01e("netfilter: ctnetlink: netns support") Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.