mm/gup_test: safely calculate GUP batch size

__gup_test_ioctl() calculates the end of a GUP batch using:

next = addr + nr * PAGE_SIZE;

If nr is too large, it can cause next to overflow and wrap around.  If it
wraps, the next > end check is bypassed and a large value of nr is passed
to the GUP call, even though the pages array was allocated according to
gup->size.  This can lead to out of bounds writes.

Also, when fewer than PAGE_SIZE bytes remain, the calculated batch
contains zero pages.  The code still calls GUP functions with pages + i,
which can point past the allocated array.

Calculate nr by taking the minimum of the number of pages per call and the
pages remaining in the address range.  Reject zero sized and non page
aligned gup->size values and zero nr_pages_per_call value.

Link: https://lore.kernel.org/20260915102524.125758-1-sarthak.sharma@arm.com
Fixes: 64c349f4ae78 ("mm: add infrastructure for get_user_pages_fast() benchmarking")
Signed-off-by: Sarthak Sharma <sarthak.sharma@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>

0 files changed, 0 insertions, 0 deletions