FAILED: patch "[PATCH] mm/hugetlb: fix use-after-free in hugetlb_mfill_atomic_pte()" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x d8a9cd7fd2fb01211430c933932da58839b8ca65
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026110447-cucumber-tummy-2f42@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d8a9cd7fd2fb01211430c933932da58839b8ca65 Mon Sep 17 00:00:00 2001
From: "David Hildenbrand (Arm)" <[email protected]>
Date: Thu, 15 Oct 2026 18:07:09 +0200
Subject: [PATCH] mm/hugetlb: fix use-after-free in hugetlb_mfill_atomic_pte()

Let's fix another instance where we use a folio after dropping the PTL, where someone else could e.g., MADV_DONTNEED it once we drop the PTL, making us trigger a use-after-free on the folio.

index 16a3abb985be..5db64fa98404 100644
@@ -6520,11 +6520,16 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
 	/* No need to invalidate - it was non-present before */
 	update_mmu_cache(dst_vma, dst_addr, dst_pte);
 
-	spin_unlock(ptl);
 	if (!is_continue)
 		folio_set_hugetlb_migratable(folio);
 	if (vm_shared || is_continue)
 		folio_unlock(folio);
+
+	/*
+	 * Hold the PTL until we're done with the folio: the page table owns the
+	 * folio reference now.
+	 */
+	spin_unlock(ptl);
 	ret = 0;
 out:
 	return ret;

From: "David Hildenbrand (Arm)" <[email protected]>

[ Upstream commit d8a9cd7fd2fb01211430c933932da58839b8ca65 ]

Let's fix another instance where we use a folio after dropping the PTL, where someone else could e.g., MADV_DONTNEED it once we drop the PTL, making us trigger a use-after-free on the folio.

---
 mm/hugetlb.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

index 947610e37a33c..e8ee7ef7fe03b 100644
@@ -5390,11 +5390,16 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 	/* No need to invalidate - it was non-present before */
 	update_mmu_cache(dst_vma, dst_addr, dst_pte);
 
-	spin_unlock(ptl);
 	if (!is_continue)
 		SetHPageMigratable(page);
 	if (vm_shared || is_continue)
 		unlock_page(page);
+
+	/*
+	 * Hold the PTL until we're done with the page: the page table owns the
+	 * page reference now.
+	 */
+	spin_unlock(ptl);
 	ret = 0;
 out:
 	return ret;

2.53.0