On Mon, Oct 10 2022 at 10:41P -0400,
Luo Meng <luomeng@xxxxxxxxxxxxxxx> wrote:
> From: Luo Meng <luomeng12@xxxxxxxxxx>
>
> If dm_get_device() create dd in multipath_message(),
> and then call table_deps() after dm_put_table_device(),
> it will lead to concurrency UAF bugs.
>
> One of the concurrency UAF can be shown as below:
>
> (USE) | (FREE)
> | target_message
> | multipath_message
> | dm_put_device
> | dm_put_table_device #
> | kfree(td) # table_device *td
> ioctl # DM_TABLE_DEPS_CMD | ...
> table_deps | ...
> dm_get_live_or_inactive_table | ...
> retrieve_dep | ...
> list_for_each_entry | ...
> deps->dev[count++] = | ...
> huge_encode_dev | ...
> (dd->dm_dev->bdev->bd_dev) | list_del(&dd->list)
> | kfree(dd) # dm_dev_internal
>
> The root cause of UAF bugs is that find_device() failed in
> dm_get_device() and will create dd and refcount set 1, kfree()
> in dm_put_table() is not protected. When td, which there are
> still pointers point to, is released, the concurrency UAF bug
> will happen.
>
> This patch add a flag to determine whether to create a new dd.
>
> Fixes: 8215d6ec5fee(dm table: remove unused dm_get_device range parameters)
> Signed-off-by: Luo Meng <luomeng12@xxxxxxxxxx>
> ---
> drivers/md/dm-mpath.c | 2 +-
> drivers/md/dm-table.c | 43 +++++++++++++++++++++--------------
> include/linux/device-mapper.h | 2 ++
> 3 files changed, 29 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index 0e325469a252..1f51059520ac 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -2001,7 +2001,7 @@ static int multipath_message(struct dm_target *ti, unsigned argc, char **argv,
> goto out;
> }
>
> - r = dm_get_device(ti, argv[1], dm_table_get_mode(ti->table), &dev);
> + r = __dm_get_device(ti, argv[1], dm_table_get_mode(ti->table), &dev, false);
> if (r) {
> DMWARN("message: error getting device %s",
> argv[1]);
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index d8034ff0cb24..ad18a41f1608 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -338,12 +338,8 @@ dev_t dm_get_dev_t(const char *path)
> }
> EXPORT_SYMBOL_GPL(dm_get_dev_t);
>
> -/*
> - * Add a device to the list, or just increment the usage count if
> - * it's already present.
> - */
> -int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
> - struct dm_dev **result)
> +int __dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
> + struct dm_dev **result, bool create_dd)
> {
> int r;
> dev_t dev;
> @@ -367,19 +363,21 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
>
> dd = find_device(&t->devices, dev);
> if (!dd) {
> - dd = kmalloc(sizeof(*dd), GFP_KERNEL);
> - if (!dd)
> - return -ENOMEM;
> -
> - if ((r = dm_get_table_device(t->md, dev, mode, &dd->dm_dev))) {
> - kfree(dd);
> - return r;
> - }
> + if (create_dd) {
> + dd = kmalloc(sizeof(*dd), GFP_KERNEL);
> + if (!dd)
> + return -ENOMEM;
>
> - refcount_set(&dd->count, 1);
> - list_add(&dd->list, &t->devices);
> - goto out;
> + if ((r = dm_get_table_device(t->md, dev, mode, &dd->dm_dev))) {
> + kfree(dd);
> + return r;
> + }
>
> + refcount_set(&dd->count, 1);
> + list_add(&dd->list, &t->devices);
> + goto out;
> + } else
> + return -ENODEV;
> } else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
> r = upgrade_mode(dd, mode, t->md);
> if (r)
> @@ -390,6 +388,17 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
> *result = dd->dm_dev;
> return 0;
> }
> +EXPORT_SYMBOL(__dm_get_device);
> +
> +/*
> + * Add a device to the list, or just increment the usage count if
> + * it's already present.
> + */
> +int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
> + struct dm_dev **result)
> +{
> + return __dm_get_device(ti, path, mode, result, true);
> +}
> EXPORT_SYMBOL(dm_get_device);
>
> static int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index 04c6acf7faaa..ef4031a844b6 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -178,6 +178,8 @@ dev_t dm_get_dev_t(const char *path);
> int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
> struct dm_dev **result);
> void dm_put_device(struct dm_target *ti, struct dm_dev *d);
> +int __dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
> + struct dm_dev **result, bool create_dd);
>
> /*
> * Information about a target type
> --
> 2.31.1
>
This patch is treating the one multipath case like it is only consumer
of dm_get_device() that might have this issue. It feels too focused on
an instance where dm_get_device()'s side-effect of creating the device
is unwelcome. Feels like you're treating the symptom rather than the
problem (e.g. that the "kfree() in dm_put_table() is not protected"?)
Mike
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