Recently, our syzbot test reported NULL pointer dereference in
device_del() by injecting memory allocation fail in device_add().
For now, callers of device_add(), such as add_disk(), may ignore
device_add()'s fail and go on working. In unregister path, it will
call device_del() from del_gendisk(). That can cause various NULL
pointer dereference, including dev->p is NULL in kill_device(),
'name' is NULL in sysfs_remove_link(), kobj->sd is 'NULL' when call
dpm_sysfs_remove(), and so on.
To avoid these kernel panic, we call device_del() only when device_add()
is success.
Signed-off-by: Yufen Yu <[email protected]>
---
drivers/base/core.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/base/core.c b/drivers/base/core.c
index f29839382f81..a10ec5dbc577 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -3380,6 +3380,9 @@ void device_del(struct device *dev)
struct class_interface *class_intf;
unsigned int noio_flag;
+ if (!dev->p)
+ return;
+
device_lock(dev);
kill_device(dev);
device_unlock(dev);
--
2.25.4
On Thu, Apr 1, 2021 at 2:56 PM Yufen Yu <[email protected]> wrote:
>
> Recently, our syzbot test reported NULL pointer dereference in
> device_del() by injecting memory allocation fail in device_add().
>
> For now, callers of device_add(), such as add_disk(), may ignore
> device_add()'s fail and go on working. In unregister path, it will
> call device_del() from del_gendisk(). That can cause various NULL
> pointer dereference, including dev->p is NULL in kill_device(),
> 'name' is NULL in sysfs_remove_link(), kobj->sd is 'NULL' when call
> dpm_sysfs_remove(), and so on.
>
> To avoid these kernel panic, we call device_del() only when device_add()
> is success.
The patch looks reasonable to me, but the above is not what it does.
It causes device_del() to be a no-op for devices that have not been
successfully added.
> Signed-off-by: Yufen Yu <[email protected]>
> ---
> drivers/base/core.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index f29839382f81..a10ec5dbc577 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3380,6 +3380,9 @@ void device_del(struct device *dev)
> struct class_interface *class_intf;
> unsigned int noio_flag;
>
> + if (!dev->p)
> + return;
> +
> device_lock(dev);
> kill_device(dev);
> device_unlock(dev);
> --
On Thu, Apr 01, 2021 at 09:01:38AM -0400, Yufen Yu wrote:
> Recently, our syzbot test reported NULL pointer dereference in
> device_del() by injecting memory allocation fail in device_add().
Don't do that :)
> For now, callers of device_add(), such as add_disk(), may ignore
> device_add()'s fail and go on working.
Please fix up those users, if device_add() fails there is no need to
call device_del().
> In unregister path, it will
> call device_del() from del_gendisk(). That can cause various NULL
> pointer dereference, including dev->p is NULL in kill_device(),
> 'name' is NULL in sysfs_remove_link(), kobj->sd is 'NULL' when call
> dpm_sysfs_remove(), and so on.
>
> To avoid these kernel panic, we call device_del() only when device_add()
> is success.
As Rafael said, that's not what you are doing here, so even if I wanted
to take this patch, I can't.
>
> Signed-off-by: Yufen Yu <[email protected]>
> ---
> drivers/base/core.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index f29839382f81..a10ec5dbc577 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3380,6 +3380,9 @@ void device_del(struct device *dev)
> struct class_interface *class_intf;
> unsigned int noio_flag;
>
> + if (!dev->p)
> + return;
Also, this isn't a good test as it's not obvious what you are trying to
check for here.
thanks,
greg k-h