[PATCH v2] firmware: dmi-sysfs: Fix null-ptr-deref in dmi_sysfs_register_handle

[Chen Zhongjin <chenzhongjin@huawei.com>]

KASAN reported a null-ptr-deref error:

KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 PID: 1373 Comm: modprobe
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
RIP: 0010:dmi_sysfs_entry_release
...
Call Trace:
 <TASK>
 kobject_put
 dmi_sysfs_register_handle (drivers/firmware/dmi-sysfs.c:540) dmi_sysfs
 dmi_decode_table (drivers/firmware/dmi_scan.c:133)
 dmi_walk (drivers/firmware/dmi_scan.c:1115)
 dmi_sysfs_init (drivers/firmware/dmi-sysfs.c:149) dmi_sysfs
 do_one_initcall (init/main.c:1296)
 ...
Kernel panic - not syncing: Fatal exception
Kernel Offset: 0x4000000 from 0xffffffff81000000
---[ end Kernel panic - not syncing: Fatal exception ]---

It is because previous patch added kobject_put() to release the memory
which will call  dmi_sysfs_entry_release() and list_del().

However, list_add_tail(entry->list) is called after the error block,
so the list_head is uninitialized and cannot be deleted.

Move error handling to after list_add_tail to fix this.

Fixes: 660ba678f999 ("firmware: dmi-sysfs: Fix memory leak in dmi_sysfs_register_handle")
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
---
v1 -> v2:
Change fix to moving error handling to after list_add_tail.
So that it is consistent with kobject_put(&entry->kobj) in other
places.
---
 drivers/firmware/dmi-sysfs.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/dmi-sysfs.c b/drivers/firmware/dmi-sysfs.c
index 66727ad3361b..402217c57033 100644
--- a/drivers/firmware/dmi-sysfs.c
+++ b/drivers/firmware/dmi-sysfs.c
@@ -603,16 +603,16 @@ static void __init dmi_sysfs_register_handle(const struct dmi_header *dh,
 	*ret = kobject_init_and_add(&entry->kobj, &dmi_sysfs_entry_ktype, NULL,
 				    "%d-%d", dh->type, entry->instance);
 
-	if (*ret) {
-		kobject_put(&entry->kobj);
-		return;
-	}
-
 	/* Thread on the global list for cleanup */
 	spin_lock(&entry_list_lock);
 	list_add_tail(&entry->list, &entry_list);
 	spin_unlock(&entry_list_lock);
 
+	if (*ret) {
+		kobject_put(&entry->kobj);
+		return;
+	}
+
 	/* Handle specializations by type */
 	switch (dh->type) {
 	case DMI_ENTRY_SYSTEM_EVENT_LOG:
-- 
2.17.1