lib/test: use after free in register_test_dev_kmod()

stable inclusion
from stable-v5.10.110
commit 327f07e3704c821ce33e54ef5046bdf69975cb86
bugzilla: https://gitee.com/openeuler/kernel/issues/I574AL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=327f07e3704c821ce33e54ef5046bdf69975cb86

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

[ Upstream commit dc0ce6cc ]

The "test_dev" pointer is freed but then returned to the caller.

Fixes: d9c6a72d ("kmod: add test driver to stress test the module loader")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NLuis Chamberlain <mcgrof@kernel.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

lib/test_kmod.c

@@ -1155,6 +1155,7 @@ static struct kmod_test_device *register_test_dev_kmod(void)
 	if (ret) {
 		pr_err("could not register misc device: %d\n", ret);
 		free_test_dev_kmod(test_dev);
+		test_dev = NULL;
 		goto out;
 	}