dm: fix a race condition in retrieve_deps

There's a race condition in the multipath target when retrieve_deps
races with multipath_message calling dm_get_device and dm_put_device.
retrieve_deps walks the list of open devices without holding any lock
but multipath may add or remove devices to the list while it is
running. The end result may be memory corruption or use-after-free
memory access.

See this description of a UAF with multipath_message():
https://listman.redhat.com/archives/dm-devel/2022-October/052373.html

Fix this bug by introducing a new rw semaphore "devices_lock". We grab
devices_lock for read in retrieve_deps and we grab it for write in
dm_get_device and dm_put_device.

Reported-by: Luo Meng <luomeng12@huawei.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Tested-by: Li Lingfeng <lilingfeng3@huawei.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
index 0d93661f88d306e0d0aa3a1ac085880a8b63d9d6..095b9b49aa8250a1f56c531883cce5f6e8a24727 100644 (file)
--- a/drivers/md/dm-core.h
+++ b/drivers/md/dm-core.h
@@ -214,6 +214,7 @@ struct dm_table {
 
        /* a list of devices used by this table */
        struct list_head devices;
+       struct rw_semaphore devices_lock;
 
        /* events get handed up using this callback */
        void (*event_fn)(void *data);

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index f5ed729a8e0cd300cd8acfb6864ae8c289da00ad..21ebb6c39394b6298ac748ffb32d11d00ad218af 100644 (file)
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1630,6 +1630,8 @@ static void retrieve_deps(struct dm_table *table,
        struct dm_dev_internal *dd;
        struct dm_target_deps *deps;
 
+       down_read(&table->devices_lock);
+
        deps = get_result_buffer(param, param_size, &len);
 
        /*
@@ -1644,7 +1646,7 @@ static void retrieve_deps(struct dm_table *table,
        needed = struct_size(deps, dev, count);
        if (len < needed) {
                param->flags |= DM_BUFFER_FULL_FLAG;
-               return;
+               goto out;
        }
 
        /*
@@ -1656,6 +1658,9 @@ static void retrieve_deps(struct dm_table *table,
                deps->dev[count++] = huge_encode_dev(dd->dm_dev->bdev->bd_dev);
 
        param->data_size = param->data_start + needed;
+
+out:
+       up_read(&table->devices_lock);
 }
 
 static int table_deps(struct file *filp, struct dm_ioctl *param, size_t param_size)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 7d208b2b1a192d88eaaec34d5247d8f7ef6273e8..37b48f63ae6a5e40b02234f214eaff487ca35e12 100644 (file)
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -135,6 +135,7 @@ int dm_table_create(struct dm_table **result, blk_mode_t mode,
                return -ENOMEM;
 
        INIT_LIST_HEAD(&t->devices);
+       init_rwsem(&t->devices_lock);
 
        if (!num_targets)
                num_targets = KEYS_PER_NODE;
@@ -359,16 +360,20 @@ int __ref dm_get_device(struct dm_target *ti, const char *path, blk_mode_t mode,
        if (dev == disk_devt(t->md->disk))
                return -EINVAL;
 
+       down_write(&t->devices_lock);
+
        dd = find_device(&t->devices, dev);
        if (!dd) {
                dd = kmalloc(sizeof(*dd), GFP_KERNEL);
-               if (!dd)
-                       return -ENOMEM;
+               if (!dd) {
+                       r = -ENOMEM;
+                       goto unlock_ret_r;
+               }
 
                r = dm_get_table_device(t->md, dev, mode, &dd->dm_dev);
                if (r) {
                        kfree(dd);
-                       return r;
+                       goto unlock_ret_r;
                }
 
                refcount_set(&dd->count, 1);
@@ -378,12 +383,17 @@ int __ref dm_get_device(struct dm_target *ti, const char *path, blk_mode_t mode,
        } else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
                r = upgrade_mode(dd, mode, t->md);
                if (r)
-                       return r;
+                       goto unlock_ret_r;
        }
        refcount_inc(&dd->count);
 out:
+       up_write(&t->devices_lock);
        *result = dd->dm_dev;
        return 0;
+
+unlock_ret_r:
+       up_write(&t->devices_lock);
+       return r;
 }
 EXPORT_SYMBOL(dm_get_device);
 
@@ -419,9 +429,12 @@ static int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
 void dm_put_device(struct dm_target *ti, struct dm_dev *d)
 {
        int found = 0;
-       struct list_head *devices = &ti->table->devices;
+       struct dm_table *t = ti->table;
+       struct list_head *devices = &t->devices;
        struct dm_dev_internal *dd;
 
+       down_write(&t->devices_lock);
+
        list_for_each_entry(dd, devices, list) {
                if (dd->dm_dev == d) {
                        found = 1;
@@ -430,14 +443,17 @@ void dm_put_device(struct dm_target *ti, struct dm_dev *d)
        }
        if (!found) {
                DMERR("%s: device %s not in table devices list",
-                     dm_device_name(ti->table->md), d->name);
-               return;
+                     dm_device_name(t->md), d->name);
+               goto unlock_ret;
        }
        if (refcount_dec_and_test(&dd->count)) {
-               dm_put_table_device(ti->table->md, d);
+               dm_put_table_device(t->md, d);
                list_del(&dd->list);
                kfree(dd);
        }
+
+unlock_ret:
+       up_write(&t->devices_lock);
 }
 EXPORT_SYMBOL(dm_put_device);