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SubjectRe: [PATCH 1/4] mtd: ubi: block: don't return on error when removing
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在 2023/5/3 0:48, Daniel Golle 写道:
> There is no point on returning the error from ubiblock_remove in case
> it is being called due to a volume removal event -- the volume is gone,
> we should destroy and remove the ubiblock device no matter what.
>
> Introduce a new boolean parameter 'force' to tell ubiblock_remove to go
> on even in case the ubiblock device is still busy. Use that new option
> when calling ubiblock_remove due to a UBI_VOLUME_REMOVED event.
>
> Signed-off-by: Daniel Golle <daniel@makrotopia.org>
> ---
> drivers/mtd/ubi/block.c | 6 +++---
> drivers/mtd/ubi/cdev.c | 2 +-
> drivers/mtd/ubi/ubi.h | 4 ++--
> 3 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/mtd/ubi/block.c b/drivers/mtd/ubi/block.c
> index 3711d7f746003..6f5804f4b8f55 100644
> --- a/drivers/mtd/ubi/block.c
> +++ b/drivers/mtd/ubi/block.c
> @@ -457,7 +457,7 @@ static void ubiblock_cleanup(struct ubiblock *dev)
> idr_remove(&ubiblock_minor_idr, dev->gd->first_minor);
> }
>
> -int ubiblock_remove(struct ubi_volume_info *vi)
> +int ubiblock_remove(struct ubi_volume_info *vi, bool force)
> {
> struct ubiblock *dev;
> int ret;
> @@ -471,7 +471,7 @@ int ubiblock_remove(struct ubi_volume_info *vi)
>
> /* Found a device, let's lock it so we can check if it's busy */
> mutex_lock(&dev->dev_mutex);
> - if (dev->refcnt > 0) {
> + if (dev->refcnt > 0 && !force) {
> ret = -EBUSY;
> goto out_unlock_dev;
> }

After looking through this series, I think we should pay attention to
one problem: The lifetime of mtd device and ubi things(ubi
device/volume/block device). It's difficult to decide whether or not to
destroy ubi things when mtd driver is removed.
If we destroy ubi things, one application may have opened an ubi volume
early, then ubi device and all its volumes are destroyed by
ubi_notify_remove(), later volume accessing by the application will
trigger an UAF problem in kernel.
App driver_remove
fd = ubi_open_volume
ubi_notify_remove
ubi_detach_mtd_dev
vfree(ubi->vtbl)
ioctl(fd, UBI_IOCVOLUP)
ubi_start_update
set_update_marker
vtbl_rec = ubi->vtbl[vol->vol_id] // UAF!

If we reserve ubi things even mtd driver is removed. There exists mtd
drivers releasing mtd device (eg. phram_remove), then upper application
could accessing released mtd device by the ubi device, which also
triggers UAF in kernel.

After looking at nvme_free_ctrl, I found that nvme_dev is released when
device refcnt becomes zero, so block device and nvme_dev won't be freed
immediately when pci driver removed if upper filesystem being mounted on
nvme device. And the mtd device's refcnt is held by ubi too, we may
follow this method, but investigating all mtd drivers looks like
unrealistic.

> @@ -546,7 +546,7 @@ static int ubiblock_notify(struct notifier_block *nb,
> */
> break;
> case UBI_VOLUME_REMOVED:
> - ubiblock_remove(&nt->vi);
> + ubiblock_remove(&nt->vi, true);
> break;
> case UBI_VOLUME_RESIZED:
> ubiblock_resize(&nt->vi);
> diff --git a/drivers/mtd/ubi/cdev.c b/drivers/mtd/ubi/cdev.c
> index f43430b9c1e65..bb55e863dd296 100644
> --- a/drivers/mtd/ubi/cdev.c
> +++ b/drivers/mtd/ubi/cdev.c
> @@ -572,7 +572,7 @@ static long vol_cdev_ioctl(struct file *file, unsigned int cmd,
> struct ubi_volume_info vi;
>
> ubi_get_volume_info(desc, &vi);
> - err = ubiblock_remove(&vi);
> + err = ubiblock_remove(&vi, false);
> break;
> }
>
> diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
> index c8f1bd4fa1008..44c0eeaf1e1b0 100644
> --- a/drivers/mtd/ubi/ubi.h
> +++ b/drivers/mtd/ubi/ubi.h
> @@ -979,7 +979,7 @@ static inline void ubi_fastmap_destroy_checkmap(struct ubi_volume *vol) {}
> int ubiblock_init(void);
> void ubiblock_exit(void);
> int ubiblock_create(struct ubi_volume_info *vi);
> -int ubiblock_remove(struct ubi_volume_info *vi);
> +int ubiblock_remove(struct ubi_volume_info *vi, bool force);
> #else
> static inline int ubiblock_init(void) { return 0; }
> static inline void ubiblock_exit(void) {}
> @@ -987,7 +987,7 @@ static inline int ubiblock_create(struct ubi_volume_info *vi)
> {
> return -ENOSYS;
> }
> -static inline int ubiblock_remove(struct ubi_volume_info *vi)
> +static inline int ubiblock_remove(struct ubi_volume_info *vi, bool force)
> {
> return -ENOSYS;
> }
>

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