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8af79d3edb
For historical reasons there are two clash resolution spots in
netfilter, one in nfnetlink_queue and one in conntrack core.
nfnetlink_queue one was added first: If a colliding entry is found, NAT
NAT transformation is reversed by calling nat engine again with altered
tuple.
See commit 368982cd7d1b ("netfilter: nfnetlink_queue: resolve clash for
unconfirmed conntracks") for details.
One problem is that nf_reroute() won't take an action if the queueing
doesn't occur in the OUTPUT hook, i.e. when queueing in forward or
postrouting, packet will be sent via the wrong path.
Another problem is that the scenario addressed (2nd UDP packet sent with
identical addresses while first packet is still being processed) can also
occur without any nfqueue involvement due to threaded resolvers doing
A and AAAA requests back-to-back.
This lead us to add clash resolution logic to the conntrack core, see
commit 6a757c07e51f ("netfilter: conntrack: allow insertion of clashing
entries"). Instead of fixing the nfqueue based logic, lets remove it
and let conntrack core handle this instead.
Retain the ->update hook for sake of nfqueue based conntrack helpers.
We could axe this hook completely but we'd have to split confirm and
helper logic again, see commit ee04805ff54a ("netfilter: conntrack: make
conntrack userspace helpers work again").
This SHOULD NOT be backported to kernels earlier than v5.6; they lack
adequate clash resolution handling.
Patch was originally written by Pablo Neira Ayuso.
Reported-by: Antonio Ojea <aojea@google.com>
Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1766
Signed-off-by: Florian Westphal <fw@strlen.de>
Tested-by: Antonio Ojea <aojea@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.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 reStructuredText markup notation.
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.