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iptables/nftables has two types of log modules: 1. backend, e.g. nf_log_syslog, which implement the functionality 2. frontend, e.g. xt_LOG or nft_log, which call the functionality provided by backend based on nf_tables or xtables rule set. Problem is that the request_module() call to load the backed in nf_logger_find_get() might happen with nftables transaction mutex held in case the call path is via nf_tables/nft_compat. This can cause deadlocks (see 'Fixes' tags for details). The chosen solution as to let modprobe deal with this by adding 'pre: ' soft dep tag to xt_LOG (to load the syslog backend) and xt_NFLOG (to load nflog backend). Eric reports that this breaks on systems with older modprobe that doesn't support softdeps. Another, similar issue occurs when someone either insmods xt_(NF)LOG directly or unloads the backend module (possible if no log frontend is in use): because the frontend module is already loaded, modprobe is not invoked again so the softdep isn't evaluated. Add a workaround: If nf_logger_find_get() returns -ENOENT and call is not via nft_compat, load the backend explicitly and try again. Else, let nft_compat ask for deferred request_module via nf_tables infra. Softdeps are kept in-place, so with newer modprobe the dependencies are resolved from userspace. Fixes:cefa31a9d4("netfilter: nft_log: perform module load from nf_tables") Fixes:a38b5b56d6("netfilter: nf_log: add module softdeps") Reported-and-tested-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Florian Westphal <fw@strlen.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.