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Eric Dumazet says: ==================== icmp: avoid possible side-channels attacks Keyu Man reminded us that linux ICMP rate limiting was still allowing side-channels attacks. Quoting the fine document [1]: 4.4 Private Source Port Scan Method ... We can then use the same global ICMP rate limit as a side channel to infer if such an ICMP message has been triggered. At first glance, this method can work but at a low speed of one port per second, due to the per-IP rate limit on ICMP messages. Surprisingly, after we analyze the source code of the ICMP rate limit implementation, we find that the global rate limit is checked prior to the per-IP rate limit. This means that even if the per-IP rate limit may eventually determine that no ICMP reply should be sent, a packet is still subjected to the global rate limit check and one token is deducted. Ironically, such a decision is consciously made by Linux developers to avoid invoking the expensive check of the per-IP rate limit [ 22], involving a search process to locate the per-IP data structure. This effectively means that the per-IP rate limit can be disre- garded for the purpose of our side channel based scan, as it only determines if the final ICMP reply is generated but has nothing to do with the global rate limit counter decrement. As a result, we can continue to use roughly the same scan method as efficient as before, achieving 1,000 ports per second ... This series : 1) Changes the order of the two rate limiters to fix the issue. 2-3) Make the 'host-wide' rate limiter a per-netns one. [1] Link: https://dl.acm.org/doi/pdf/10.1145/3372297.3417280 ==================== Link: https://patch.msgid.link/20240829144641.3880376-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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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.