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commit 873aefb376 upstream.
There's currently a reference count leak on the zero page. We increment
the reference via pin_user_pages_remote(), but the page is later handled
as an invalid/reserved page, therefore it's not accounted against the
user and not unpinned by our put_pfn().
Introducing special zero page handling in put_pfn() would resolve the
leak, but without accounting of the zero page, a single user could
still create enough mappings to generate a reference count overflow.
The zero page is always resident, so for our purposes there's no reason
to keep it pinned. Therefore, add a loop to walk pages returned from
pin_user_pages_remote() and unpin any zero pages.
Cc: stable@vger.kernel.org
Reported-by: Luboslav Pivarc <lpivarc@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/166182871735.3518559.8884121293045337358.stgit@omen
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.