Subject: CVE-2023-52909: nfsd: fix handling of cached open files in nfsd4_open codepath

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

nfsd: fix handling of cached open files in nfsd4_open codepath

Commit fb70bf124b05 ("NFSD: Instantiate a struct file when creating a
regular NFSv4 file") added the ability to cache an open fd over a
compound. There are a couple of problems with the way this currently
works:

It's racy, as a newly-created nfsd_file can end up with its PENDING bit
cleared while the nf is hashed, and the nf_file pointer is still zeroed
out. Other tasks can find it in this state and they expect to see a
valid nf_file, and can oops if nf_file is NULL.

Also, there is no guarantee that we'll end up creating a new nfsd_file
if one is already in the hash. If an extant entry is in the hash with a
valid nf_file, nfs4_get_vfs_file will clobber its nf_file pointer with
the value of op_file and the old nf_file will leak.

Fix both issues by making a new nfsd_file_acquirei_opened variant that
takes an optional file pointer. If one is present when this is called,
we'll take a new reference to it instead of trying to open the file. If
the nfsd_file already has a valid nf_file, we'll just ignore the
optional file and pass the nfsd_file back as-is.

Also rework the tracepoints a bit to allow for an "opened" variant and
don't try to avoid counting acquisitions in the case where we already
have a cached open file.

The Linux kernel CVE team has assigned CVE-2023-52909 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.19 with commit fb70bf124b05 and fixed in 6.1.7 with commit 973acfdfe90c
	Issue introduced in 5.19 with commit fb70bf124b05 and fixed in 6.2 with commit 0b3a551fa58b

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2023-52909
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	fs/nfsd/filecache.c
	fs/nfsd/filecache.h
	fs/nfsd/nfs4state.c
	fs/nfsd/trace.h

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/45c08a752982116f3287afcd1bd9c50f4fab0c28
	https://git.kernel.org/stable/c/0b778361998d6c6356b8d2fc7ddf025fb3224654
	https://git.kernel.org/stable/c/973acfdfe90c8a4e58ade97ff0653a498531ff2e
	https://git.kernel.org/stable/c/0b3a551fa58b4da941efeb209b3770868e2eddd7