Re: [PATCH] block: add allocation size check in blkdev_pr_read_keys()

[Deepanshu Kartikey]

On Fri, Dec 12, 2025 at 11:46 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> Well, bother checks for sure are redundant.  But maybe this is also
> a good chance to pick a sane arbitrary limited instead of
> KMALLOC_MAX_SIZE.  And if that is above KMALLOC_MAX_SIZE, switch to
> using kvzalloc.
>

Thanks for the feedback.

How about limiting num_keys to 64K (1u << 16)? In practice, PR keys
are used for shared storage coordination and typical deployments have
only a handful of hosts, so this should be more than enough for any
realistic use case.

With a bounded num_keys, the SIZE_MAX check becomes unnecessary, so
I've removed it. Also switched to kvzalloc/kvfree to handle larger
allocations gracefully.

Something like below:

+/* Limit the number of keys to prevent excessive memory allocation */
+#define PR_KEYS_MAX_NUM (1u << 16)
+
 static int blkdev_pr_read_keys(struct block_device *bdev, blk_mode_t mode,
  struct pr_read_keys __user *arg)
 {
...

  if (copy_from_user(&read_keys, arg, sizeof(read_keys)))
  return -EFAULT;

+ if (read_keys.num_keys > PR_KEYS_MAX_NUM)
+ return -EINVAL;
+
  keys_info_len = struct_size(keys_info, keys, read_keys.num_keys);
- if (keys_info_len == SIZE_MAX)
- return -EINVAL;

- keys_info = kzalloc(keys_info_len, GFP_KERNEL);
+ keys_info = kvzalloc(keys_info_len, GFP_KERNEL);
  if (!keys_info)
  return -ENOMEM;

...

 out:
- kfree(keys_info);
+ kvfree(keys_info);
  return ret;
 }