RE: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in __nbd_ioctl()

David Laight
2021-09-14T08:14:17Z

...
>         case NBD_SET_SIZE:
>                 return nbd_set_size(nbd, arg, config->blksize);
>         case NBD_SET_SIZE_BLOCKS:
> -               if (check_mul_overflow((loff_t)arg, config->blksize,
> &bytesize))
> +               if (arg && (LLONG_MAX / arg <= config->blksize))
>                         return -EINVAL;
> -               return nbd_set_size(nbd, bytesize, config->blksize);
> +               return nbd_set_size(nbd, arg * config->blksize,
> +                                   config->blksize);

Shouldn't there just be sanity bound checks on 'config->blksize' and
'arg' so that the product is never going to overflow?

It isn't as though any values near the overflow limit are sane.

I suspect you could check config->blksize <= 64k && arg <= 32k
and even that would be generous.

David

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