test_firmware: fix end of loop test in upload_read_show()

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")
Reviewed-by: Russ Weight <russell.h.weight@intel.com>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YnTGU3UJOIA09I7e@kili
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/lib/test_firmware.c b/lib/test_firmware.c
index 76115c1..c82b659 100644 (file)
--- 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;