mm/hmm/test: reject overflowing page counts

The number of pages comes directly from userspace.  Shifting a value
larger than ULONG_MAX >> PAGE_SHIFT discards its high bits before the
existing end-address check.  A request for a huge number of pages can
therefore be accepted and processed as a much smaller request.

Reject page counts that cannot be represented as a byte size before
performing the shift.

So far as ChatGPT and I can tell this doesn't cause an issue in practice
but preventing this integer overflow is the correct thing to do.

Link: https://lore.kernel.org/6f0d39089e938d4f53dc72632eb84aca34de7015.1789457465.git.error27@gmail.com
Fixes: b2ef9f5a5cb3 ("mm/hmm/test: add selftest driver for HMM")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Assisted-by: ChatGPT:gpt-5
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Wei Yongjun <weiyongjun1@huawei.com>

0 files changed, 0 insertions, 0 deletions