+ mm-hmm-test-reject-overflowing-page-counts.patch added to mm-new branch

+ mm-hmm-test-reject-overflowing-page-counts.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/hmm/test: reject overflowing page counts
has been added to the -mm mm-new branch.  Its filename is
     mm-hmm-test-reject-overflowing-page-counts.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hmm-test-reject-overflowing-page-counts.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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and is updated there most days

------------------------------------------------------
From: Dan Carpenter <error27@gmail.com>
Subject: mm/hmm/test: reject overflowing page counts
Date: Tue, 15 Sep 2026 19:37:27 +0300

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>
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>
Assisted-by: ChatGPT:gpt-5
---

 lib/test_hmm.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/lib/test_hmm.c~mm-hmm-test-reject-overflowing-page-counts
+++ a/lib/test_hmm.c
@@ -1624,6 +1624,8 @@ static long dmirror_fops_unlocked_ioctl(
 
 	if (cmd.addr & ~PAGE_MASK)
 		return -EINVAL;
+	if (cmd.npages > ULONG_MAX >> PAGE_SHIFT)
+		return -EINVAL;
 	if (cmd.addr >= (cmd.addr + (cmd.npages << PAGE_SHIFT)))
 		return -EINVAL;
 
_

Patches currently in -mm which might be from error27@gmail.com are

mm-hmm-test-reject-overflowing-page-counts.patch