[PATCH v3] test_firmware: fix end of loop test in upload_read_show()

[Dan Carpenter <dan.carpenter@oracle.com>]

If a list_for_each_entry() loop exits without hitting a break statement
then the iterator points to invalid memory.  So in this code the
"tst->name" dereference is an out bounds read.  It's an offset from the
&test_upload_list pointer and it will likely work fine most of the time
but it's not correct.

One alternative is to fix this this by changing the test to:

	if (list_entry_is_head(tst, &test_upload_list, node)) {

But the simpler, trendy new way is just create a new variable and test
for NULL.

Fixes: a31ad463b72d ("test_firmware: Add test support for firmware upload")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Russ Weight <russell.h.weight@intel.com>
---
v3: Add Russ's Reviewed-by tag and this --- revision text
v2: Change the commit message

 lib/test_firmware.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/lib/test_firmware.c b/lib/test_firmware.c
index 76115c1a2629..c82b65947ce6 100644
--- a/lib/test_firmware.c
+++ b/lib/test_firmware.c
@@ -1392,7 +1392,8 @@ static ssize_t upload_read_show(struct device *dev,
 				struct device_attribute *attr,
 				char *buf)
 {
-	struct test_firmware_upload *tst;
+	struct test_firmware_upload *tst = NULL;
+	struct test_firmware_upload *tst_iter;
 	int ret = -EINVAL;
 
 	if (!test_fw_config->upload_name) {
@@ -1401,11 +1402,13 @@ static ssize_t upload_read_show(struct device *dev,
 	}
 
 	mutex_lock(&test_fw_mutex);
-	list_for_each_entry(tst, &test_upload_list, node)
-		if (tst->name == test_fw_config->upload_name)
+	list_for_each_entry(tst_iter, &test_upload_list, node)
+		if (tst_iter->name == test_fw_config->upload_name) {
+			tst = tst_iter;
 			break;
+		}
 
-	if (tst->name != test_fw_config->upload_name) {
+	if (!tst) {
 		pr_err("Firmware name not found: %s\n",
 		       test_fw_config->upload_name);
 		goto out;
-- 
2.35.1