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Eric W. Biederman f9d87929d4 ucount: Make get_ucount a safe get_user replacement
When the ucount code was refactored to create get_ucount it was missed
that some of the contexts in which a rlimit is kept elevated can be
the only reference to the user/ucount in the system.

Ordinary ucount references exist in places that also have a reference
to the user namspace, but in POSIX message queues, the SysV shm code,
and the SIGPENDING code there is no independent user namespace
reference.

Inspection of the the user_namespace show no instance of circular
references between struct ucounts and the user_namespace.  So
hold a reference from struct ucount to i's user_namespace to
resolve this problem.

Link: https://lore.kernel.org/lkml/YZV7Z+yXbsx9p3JN@fixkernel.com/
Reported-by: Qian Cai <quic_qiancai@quicinc.com>
Reported-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Reviewed-by: Mathias Krause <minipli@grsecurity.net>
Reviewed-by: Alexey Gladkov <legion@kernel.org>
Fixes: d646969055 ("Reimplement RLIMIT_SIGPENDING on top of ucounts")
Fixes: 6e52a9f053 ("Reimplement RLIMIT_MSGQUEUE on top of ucounts")
Fixes: d7c9e99aee ("Reimplement RLIMIT_MEMLOCK on top of ucounts")
Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
History 2022-01-26 18:34:11 -06:00
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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 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.