CVE-2021-47316: nfsd: fix NULL dereference in nfs3svc_encode_getaclres

CVE-2021-47316: nfsd: fix NULL dereference in nfs3svc_encode_getaclres

[Greg Kroah-Hartman]

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

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

nfsd: fix NULL dereference in nfs3svc_encode_getaclres

In error cases the dentry may be NULL.

Before 20798dfe249a, the encoder also checked dentry and
d_really_is_positive(dentry), but that looks like overkill to me--zero
status should be enough to guarantee a positive dentry.

This isn't the first time we've seen an error-case NULL dereference
hidden in the initialization of a local variable in an xdr encoder.  But
I went back through the other recent rewrites and didn't spot any
similar bugs.

The Linux kernel CVE team has assigned CVE-2021-47316 to this issue.


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

	Issue introduced in 5.13 with commit 20798dfe249a and fixed in 5.13.4 with commit 650e6f383a6e
	Issue introduced in 5.13 with commit 20798dfe249a and fixed in 5.14 with commit ab1016d39cc0

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-2021-47316
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/nfs3acl.c


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/650e6f383a6eb40f7c0a010982a74ab4b6893870
	https://git.kernel.org/stable/c/ab1016d39cc052064e32f25ad18ef8767a0ee3b8