The patch titled Subject: mm/memfd: fix information leak in hugetlb folios has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-memfd-fix-information-leak-in-hugetlb-folios.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Deepanshu Kartikey kartikey406@gmail.com Subject: mm/memfd: fix information leak in hugetlb folios Date: Wed, 12 Nov 2025 20:20:34 +0530
When allocating hugetlb folios for memfd, three initialization steps are missing:
1. Folios are not zeroed, leading to kernel memory disclosure to userspace 2. Folios are not marked uptodate before adding to page cache 3. hugetlb_fault_mutex is not taken before hugetlb_add_to_page_cache()
The memfd allocation path bypasses the normal page fault handler (hugetlb_no_page) which would handle all of these initialization steps. This is problematic especially for udmabuf use cases where folios are pinned and directly accessed by userspace via DMA.
Fix by matching the initialization pattern used in hugetlb_no_page(): - Zero the folio using folio_zero_user() which is optimized for huge pages - Mark it uptodate with folio_mark_uptodate() - Take hugetlb_fault_mutex before adding to page cache to prevent races
The folio_zero_user() change also fixes a potential security issue where uninitialized kernel memory could be disclosed to userspace through read() or mmap() operations on the memfd.
Link: https://lkml.kernel.org/r/20251112145034.2320452-1-kartikey406@gmail.com Fixes: 89c1905d9c14 ("mm/gup: introduce memfd_pin_folios() for pinning memfd folios") Signed-off-by: Deepanshu Kartikey kartikey406@gmail.com Reported-by: syzbot+f64019ba229e3a5c411b@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/20251112031631.2315651-1-kartikey406@gmail.com/ [v1] Closes: https://syzkaller.appspot.com/bug?extid=f64019ba229e3a5c411b Suggested-by: Oscar Salvador osalvador@suse.de Suggested-by: David Hildenbrand david@redhat.com Tested-by: syzbot+f64019ba229e3a5c411b@syzkaller.appspotmail.com Cc: Vivek Kasireddy vivek.kasireddy@intel.com Cc: Jason Gunthorpe jgg@nvidia.com Cc: Jason Gunthorpe jgg@nvidia.com (v2) Cc: Christoph Hellwig hch@lst.de (v6) Cc: Dave Airlie airlied@redhat.com Cc: Gerd Hoffmann kraxel@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/memfd.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+)
--- a/mm/memfd.c~mm-memfd-fix-information-leak-in-hugetlb-folios +++ a/mm/memfd.c @@ -96,9 +96,36 @@ struct folio *memfd_alloc_folio(struct f NULL, gfp_mask); if (folio) { + u32 hash; + + /* + * Zero the folio to prevent information leaks to userspace. + * Use folio_zero_user() which is optimized for huge/gigantic + * pages. Pass 0 as addr_hint since this is not a faulting path + * and we don't have a user virtual address yet. + */ + folio_zero_user(folio, 0); + + /* + * Mark the folio uptodate before adding to page cache, + * as required by filemap.c and other hugetlb paths. + */ + __folio_mark_uptodate(folio); + + /* + * Serialize hugepage allocation and instantiation to prevent + * races with concurrent allocations, as required by all other + * callers of hugetlb_add_to_page_cache(). + */ + hash = hugetlb_fault_mutex_hash(memfd->f_mapping, idx); + mutex_lock(&hugetlb_fault_mutex_table[hash]); + err = hugetlb_add_to_page_cache(folio, memfd->f_mapping, idx); + + mutex_unlock(&hugetlb_fault_mutex_table[hash]); + if (err) { folio_put(folio); goto err_unresv; _
Patches currently in -mm which might be from kartikey406@gmail.com are
mm-memfd-fix-information-leak-in-hugetlb-folios.patch ocfs2-validate-cl_bpc-in-allocator-inodes-to-prevent-divide-by-zero.patch