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SubjectRe: [PATCH] firmware: dmi-sysfs: Fix null-ptr-deref in dmi_sysfs_register_handle
On Mon, Oct 17, 2022 at 05:53:42PM +0800, Chen Zhongjin wrote:
> 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.
>
> Because entry is allocated by kzalloc() so the list.prev is NULL in
> the error path. Check it in dmi_sysfs_entry_release() to avoid
> deleting uninitialized list_head.
>
> Fixes: 660ba678f999 ("firmware: dmi-sysfs: Fix memory leak in dmi_sysfs_register_handle")
>
> Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
> ---
> drivers/firmware/dmi-sysfs.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/firmware/dmi-sysfs.c b/drivers/firmware/dmi-sysfs.c
> index 66727ad3361b..f8815eeed00c 100644
> --- a/drivers/firmware/dmi-sysfs.c
> +++ b/drivers/firmware/dmi-sysfs.c
> @@ -557,9 +557,12 @@ static void dmi_sysfs_entry_release(struct kobject *kobj)
> {
> struct dmi_sysfs_entry *entry = to_entry(kobj);
>
> - spin_lock(&entry_list_lock);
> - list_del(&entry->list);
> - spin_unlock(&entry_list_lock);
> + if (entry->list.prev != NULL) {

You should not be poking around in a lock structure like this at all.
Also the lock isn't held, so how do you know this is going to work?

I suggest fixing up the original patch, perhaps reverting that instead?

thanks,

greg k-h

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