[PATCH 4.15 191/202] acpi, nfit: fix register dimm error handling

[Greg Kroah-Hartman]

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Toshi Kani <toshi.kani@xxxxxxx>

commit 23fbd7c70aec7600e3227eb24259fc55bf6e4881 upstream.

A NULL pointer reference kernel bug was observed when
acpi_nfit_add_dimm() called in acpi_nfit_register_dimms() failed. This
error path does not set nfit_mem->nvdimm, but the 2nd
list_for_each_entry() loop in the function assumes it's always set. Add
a check to nfit_mem->nvdimm.

Fixes: ba9c8dd3c222 ("acpi, nfit: add dimm device notification support")
Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/acpi/nfit/core.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -1867,6 +1867,9 @@ static int acpi_nfit_register_dimms(stru
 		struct kernfs_node *nfit_kernfs;
 
 		nvdimm = nfit_mem->nvdimm;
+		if (!nvdimm)
+			continue;
+
 		nfit_kernfs = sysfs_get_dirent(nvdimm_kobj(nvdimm)->sd, "nfit");
 		if (nfit_kernfs)
 			nfit_mem->flags_attr = sysfs_get_dirent(nfit_kernfs,