at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-clear-page-private-in-split_page-for-tail-pages.patch

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

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------------------------------------------------------
From: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Subject: mm/page_alloc: clear page->private in split_page() for tail pages
Date: Fri, 6 Feb 2026 22:40:17 +0500

When vmalloc allocates high-order pages and splits them via split_page(),
tail pages may retain stale page->private values from previous use by the
buddy allocator.

This causes a use-after-free in the swap subsystem. The swap code uses
vmalloc_to_page() to get struct page pointers for swap_map, then uses
page->private to track swap count continuations. In add_swap_count_
continuation(), the condition "if (!page_private(head))" assumes fresh
pages have page->private == 0, but tail pages from split_page() may have
non-zero stale values.

When page->private accidentally contains a value like SWP_CONTINUED (32),
swap_count_continued() incorrectly assumes the continuation list is valid
and iterates over uninitialized page->lru, which may contain LIST_POISON
values from a previous list_del(), causing a crash:

  KASAN: maybe wild-memory-access in range [0xdead000000000100-0xdead000000000107]
  RIP: 0010:__do_sys_swapoff+0x1151/0x1860

Fix this by clearing page->private for tail pages in split_page(). Note
that we don't touch page->lru to avoid breaking split_free_page() which
may have the head page on a list.

Link: https://lkml.kernel.org/r/20260206174017.128673-1-mikhail.v.gavrilov@gmail.com
Fixes: 3b8000ae185c ("mm/vmalloc: huge vmalloc backing pages should be split rather than compound")
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-clear-page-private-in-split_page-for-tail-pages
+++ a/mm/page_alloc.c
@@ -3129,9 +3129,14 @@ void split_page(struct page *page, unsig
 
 	VM_WARN_ON_PAGE(!page_count(page), page);
 
-	for (i = 1; i < (1 << order); i++)
+	for (i = 1; i < (1 << order); i++) {
 		set_page_refcounted(page + i);
-
+		/*
+		 * Tail pages may have stale page->private from buddy
+		 * allocator or previous use. Clear it.
+		 */
+		set_page_private(page + i, 0);
+	}
 	__split_page(page, order);
 }
 EXPORT_SYMBOL_GPL(split_page);
_

Patches currently in -mm which might be from mikhail.v.gavrilov@gmail.com are

mm-page_alloc-clear-page-private-in-split_page-for-tail-pages.patch+ mm-page_alloc-clear-page-private-in-split_page-for-tail-pages.patch added to mm-unstable branchAndrew Morton <akpm@linux-foundation.org> undefinedmm-commits@vger.kernel.org,ziy@nvidia.com,vbabka@suse.cz,surenb@google.com,stable@vger.kernel.org,ryncsn@gmail.com,mhocko@suse.com,jackmanb@google.com,hughd@google.com,hannes@cmpxchg.org,chrisl@kernel.org,mikhail.v.gavrilov@gmail.com,akpm@linux-foundation.org undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined