[bug report] bpf: Add generic support for update and delete batch ops

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Brian Vazquez,

The patch aa2e93b8e58e: "bpf: Add generic support for update and
delete batch ops" from Jan 15, 2020, leads to the following static
checker warning:

	kernel/bpf/syscall.c:1322 generic_map_update_batch()
	error: 'key' dereferencing possible ERR_PTR()

kernel/bpf/syscall.c
  1296  
  1297          value = kmalloc(value_size, GFP_USER | __GFP_NOWARN);
  1298          if (!value)
  1299                  return -ENOMEM;
  1300  
  1301          for (cp = 0; cp < max_count; cp++) {
  1302                  key = __bpf_copy_key(keys + cp * map->key_size, map->key_size);
  1303                  if (IS_ERR(key)) {
  1304                          err = PTR_ERR(key);
  1305                          break;
                                ^^^^^
This will Oops.

  1306                  }
  1307                  err = -EFAULT;
  1308                  if (copy_from_user(value, values + cp * value_size, value_size))
  1309                          break;
  1310  
  1311                  err = bpf_map_update_value(map, f, key, value,
  1312                                             attr->batch.elem_flags);
  1313  
  1314                  if (err)
  1315                          break;

But the success path seems to leak.  Anyway, either we free the last
successful key or we are leaking so this doesn't seem workable.  Does
map->key_size change?  Maybe move the allocation from __bpf_copy_key()
to before the start of the loop.

  1316          }
  1317  
  1318          if (copy_to_user(&uattr->batch.count, &cp, sizeof(cp)))
  1319                  err = -EFAULT;
  1320  
  1321          kfree(value);
  1322          kfree(key);
  1323          return err;
  1324  }

regards,
dan carpenter