CVE-2022-49353: powerpc/papr_scm: don't requests stats with '0' sized stats buffer

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

powerpc/papr_scm: don't requests stats with '0' sized stats buffer

Sachin reported [1] that on a POWER-10 lpar he is seeing a kernel panic being
reported with vPMEM when papr_scm probe is being called. The panic is of the
form below and is observed only with following option disabled(profile) for the
said LPAR 'Enable Performance Information Collection' in the HMC:

 Kernel attempted to write user page (1c) - exploit attempt? (uid: 0)
 BUG: Kernel NULL pointer dereference on write at 0x0000001c
 Faulting instruction address: 0xc008000001b90844
 Oops: Kernel access of bad area, sig: 11 [#1]
<snip>
 NIP [c008000001b90844] drc_pmem_query_stats+0x5c/0x270 [papr_scm]
 LR [c008000001b92794] papr_scm_probe+0x2ac/0x6ec [papr_scm]
 Call Trace:
       0xc00000000941bca0 (unreliable)
       papr_scm_probe+0x2ac/0x6ec [papr_scm]
       platform_probe+0x98/0x150
       really_probe+0xfc/0x510
       __driver_probe_device+0x17c/0x230
<snip>
 ---[ end trace 0000000000000000 ]---
 Kernel panic - not syncing: Fatal exception

On investigation looks like this panic was caused due to a 'stat_buffer' of
size==0 being provided to drc_pmem_query_stats() to fetch all performance
stats-ids of an NVDIMM. However drc_pmem_query_stats() shouldn't have been called
since the vPMEM NVDIMM doesn't support and performance stat-id's. This was caused
due to missing check for 'p->stat_buffer_len' at the beginning of
papr_scm_pmu_check_events() which indicates that the NVDIMM doesn't support
performance-stats.

Fix this by introducing the check for 'p->stat_buffer_len' at the beginning of
papr_scm_pmu_check_events().

[1] https://lore.kernel.org/all/6B3A522A-6A5F-4CC9-B268-0C63AA6E07D3@linux.ibm.com

The Linux kernel CVE team has assigned CVE-2022-49353 to this issue.


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

	Issue introduced in 5.18.3 with commit b073096df4dec70d0436321b7093bad27ae91f9e and fixed in 5.18.4 with commit e1295aab2ebcda1c1a9ed342baedc080e5c393e5

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-2022-49353
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:
	arch/powerpc/platforms/pseries/papr_scm.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/e1295aab2ebcda1c1a9ed342baedc080e5c393e5
	https://git.kernel.org/stable/c/07bf9431b1590d1cd7a8d62075d0b50b073f0495