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NFSD has always supported added network listeners. The new netlink protocol now enables the removal of listeners. Olga noticed that if an RDMA listener is removed and immediately re-added, the deferred __svc_rdma_free() function might not have run yet, so some or all of the old listener's RDMA resources linger, which prevents a new listener on the same address from being created. Also, svc_xprt_free() does a module_put() just after calling ->xpo_free(). That means if there is deferred work going on, the module could be unloaded before that work is even started, resulting in a UAF. Neil asks: > What particular part of __svc_rdma_free() needs to run in order for a > subsequent registration to succeed? > Can that bit be run directory from svc_rdma_free() rather than be > delayed? > (I know almost nothing about rdma so forgive me if the answers to these > questions seems obvious) The reasons I can recall are: - Some of the transport tear-down work can sleep - Releasing a cm_id is tricky and can deadlock We might be able to mitigate the second issue with judicious application of transport reference counting. Reported-by: Olga Kornievskaia <okorniev@redhat.com> Closes: https://lore.kernel.org/linux-nfs/20250821204328.89218-1-okorniev@redhat.com/ Suggested-by: NeilBrown <neil@brown.name> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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.