PCI/sysfs: Fix dsm_label_utf16s_to_utf8s() buffer overrun

stable inclusion
from linux-4.19.198
commit 1b78ad07da08ca15c47af0669d5a4e4f896cbb3c

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

[ Upstream commit bdcdaa13 ]

"utf16s_to_utf8s(..., buf, PAGE_SIZE)" puts up to PAGE_SIZE bytes into
"buf" and returns the number of bytes it actually put there.  If it wrote
PAGE_SIZE bytes, the newline added by dsm_label_utf16s_to_utf8s() would
overrun "buf".

Reduce the size available for utf16s_to_utf8s() to use so there is always
space for the newline.

[bhelgaas: reorder patch in series, commit log]
Fixes: 6058989b ("PCI: Export ACPI _DSM provided firmware instance number and string name to sysfs")
Link: https://lore.kernel.org/r/20210603000112.703037-7-kw@linux.comReported-by: NJoe Perches <joe@perches.com>
Signed-off-by: NKrzysztof Wilczyński <kw@linux.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/pci/pci-label.c

@@ -162,7 +162,7 @@ static void dsm_label_utf16s_to_utf8s(union acpi_object *obj, char *buf)
 	len = utf16s_to_utf8s((const wchar_t *)obj->buffer.pointer,
 			      obj->buffer.length,
 			      UTF16_LITTLE_ENDIAN,
-			      buf, PAGE_SIZE);
+			      buf, PAGE_SIZE - 1);
 	buf[len] = '\n';
 }