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If we receive a SYN packet in original direction on an existing connection tracking entry, we let this SYN through because conntrack might be out-of-sync. Conntrack gets back in sync when server responds with SYN/ACK and state gets updated accordingly. However, if server replies with RST, this packet might be marked as INVALID because td_maxack value reflects the *old* conntrack state and not the state of the originator of the RST. Avoid td_maxack-based checks if previous packet was a SYN. Unfortunately that is not be enough: an out of order ACK in original direction updates last_index, so we still end up marking valid RST. Thus disable the sequence check when we are not in established state and the received RST has a sequence of 0. Because marking RSTs as invalid usually leads to unwanted timeouts, also skip RST sequence checks if a conntrack entry is already closing. Such entries can already be evicted via GC in case the table is full. Co-developed-by: Florian Westphal <fw@strlen.de> Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Ali Abdallah <aabdallah@suse.de> 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 Restructured Text 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.