Subject: CVE-2021-47290: scsi: target: Fix NULL dereference on XCOPY completion

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

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

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

scsi: target: Fix NULL dereference on XCOPY completion

CPU affinity control added with commit 39ae3edda325 ("scsi: target: core:
Make completion affinity configurable") makes target_complete_cmd() queue
work on a CPU based on se_tpg->se_tpg_wwn->cmd_compl_affinity state.

LIO's EXTENDED COPY worker is a special case in that read/write cmds are
dispatched using the global xcopy_pt_tpg, which carries a NULL se_tpg_wwn
pointer following initialization in target_xcopy_setup_pt().

The NULL xcopy_pt_tpg->se_tpg_wwn pointer is dereferenced on completion of
any EXTENDED COPY initiated read/write cmds. E.g using the libiscsi
SCSI.ExtendedCopy.Simple test:

  BUG: kernel NULL pointer dereference, address: 00000000000001a8
  RIP: 0010:target_complete_cmd+0x9d/0x130 [target_core_mod]
  Call Trace:
   fd_execute_rw+0x148/0x42a [target_core_file]
   ? __dynamic_pr_debug+0xa7/0xe0
   ? target_check_reservation+0x5b/0x940 [target_core_mod]
   __target_execute_cmd+0x1e/0x90 [target_core_mod]
   transport_generic_new_cmd+0x17c/0x330 [target_core_mod]
   target_xcopy_issue_pt_cmd+0x9/0x60 [target_core_mod]
   target_xcopy_read_source.isra.7+0x10b/0x1b0 [target_core_mod]
   ? target_check_fua+0x40/0x40 [target_core_mod]
   ? transport_complete_task_attr+0x130/0x130 [target_core_mod]
   target_xcopy_do_work+0x61f/0xc00 [target_core_mod]

This fix makes target_complete_cmd() queue work on se_cmd->cpuid if
se_tpg_wwn is NULL.

The Linux kernel CVE team has assigned CVE-2021-47290 to this issue.

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

	Issue introduced in 5.13 with commit 39ae3edda325 and fixed in 5.13.6 with commit e7732c5a19a1
	Issue introduced in 5.13 with commit 39ae3edda325 and fixed in 5.14 with commit a47fa41381a0

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-2021-47290
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:
	drivers/target/target_core_transport.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/e7732c5a19a15a62b0b23fd683a639b0483e1f40
	https://git.kernel.org/stable/c/a47fa41381a09e5997afd762664db4f5f6657e03