kernel/linux.git/mm/memfd.c, branch v6.18.21

mm/memfd: fix information leak in hugetlb folios

2025-11-24T22:25:17+00:00

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 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 Suggested-by: David Hildenbrand Tested-by: syzbot+f64019ba229e3a5c411b@syzkaller.appspotmail.com Acked-by: Oscar Salvador Acked-by: David Hildenbrand (Red Hat) Acked-by: Hugh Dickins Cc: Vivek Kasireddy Cc: Jason Gunthorpe Cc: Jason Gunthorpe (v2) Cc: Christoph Hellwig (v6) Cc: Dave Airlie Cc: Gerd Hoffmann Cc: Signed-off-by: Andrew Morton

mm/memfd: remove redundant casts

2025-09-21T21:22:00+00:00

MFD_ALL_FLAGS is already an unsigned int. Remove redundant casts to unsigned int. Link: https://lkml.kernel.org/r/efbbe6093b64a5b19f974871d5262d6e75dff2c0.1756639225.git.joeypabalinas@gmail.com Signed-off-by: Joey Pabalinas Cc: Baolin Wang Cc: Hugh Dickins Cc: Joey Pabalinas Signed-off-by: Andrew Morton

mm/memfd: replace deprecated strcpy() with memcpy() in alloc_name()

2025-07-20T01:59:57+00:00

strcpy() is deprecated; use memcpy() instead. Not copying the NUL terminator is safe because strncpy_from_user() would overwrite it anyway by appending uname to the destination buffer at index MFD_NAME_PREFIX_LEN. No functional changes intended. Link: https://github.com/KSPP/linux/issues/88 Link: https://lkml.kernel.org/r/20250712174516.64243-2-thorsten.blum@linux.dev Signed-off-by: Thorsten Blum Cc: Baolin Wang Cc: Hugh Dickins Signed-off-by: Andrew Morton

mm/memfd: reserve hugetlb folios before allocation

2025-07-10T05:42:15+00:00

When we try to allocate a folio via alloc_hugetlb_folio_reserve(), we need to ensure that there is an active reservation associated with the allocation. Otherwise, our allocation request would fail if there are no active reservations made at that moment against any other allocations. This is because alloc_hugetlb_folio_reserve() checks h->resv_huge_pages before proceeding with the allocation. Therefore, to address this issue, we just need to make a reservation (by calling hugetlb_reserve_pages()) before we try to allocate the folio. This will also ensure that proper region/subpool accounting is done associated with our allocation. Link: https://lkml.kernel.org/r/20250618053415.1036185-3-vivek.kasireddy@intel.com Signed-off-by: Vivek Kasireddy Cc: Steve Sistare Cc: Muchun Song Cc: David Hildenbrand Cc: Gerd Hoffmann Cc: Oscar Salvador Signed-off-by: Andrew Morton

mm: update core kernel code to use vm_flags_t consistently

2025-07-10T05:42:13+00:00

The core kernel code is currently very inconsistent in its use of vm_flags_t vs. unsigned long. This prevents us from changing the type of vm_flags_t in the future and is simply not correct, so correct this. While this results in rather a lot of churn, it is a critical pre-requisite for a future planned change to VMA flag type. Additionally, update VMA userland tests to account for the changes. To make review easier and to break things into smaller parts, driver and architecture-specific changes is left for a subsequent commit. The code has been adjusted to cascade the changes across all calling code as far as is needed. We will adjust architecture-specific and driver code in a subsequent patch. Overall, this patch does not introduce any functional change. Link: https://lkml.kernel.org/r/d1588e7bb96d1ea3fe7b9df2c699d5b4592d901d.1750274467.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes Acked-by: Kees Cook Acked-by: Mike Rapoport (Microsoft) Acked-by: Jan Kara Acked-by: Christian Brauner Reviewed-by: Vlastimil Babka Acked-by: Oscar Salvador Reviewed-by: Pedro Falcato Acked-by: Zi Yan Acked-by: David Hildenbrand Reviewed-by: Anshuman Khandual Cc: Jann Horn Cc: Liam R. Howlett Cc: Catalin Marinas Cc: Jarkko Sakkinen Signed-off-by: Andrew Morton

mm: use folio_expected_ref_count() helper for reference counting

2025-07-10T05:42:08+00:00

Replace open-coded folio reference count calculations with the folio_expected_ref_count(). No functional changes intended. Link: https://lkml.kernel.org/r/20250611052706.515408-2-shivankg@amd.com Signed-off-by: Shivank Garg Acked-by: David Hildenbrand Reviewed-by: Oscar Salvador Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Alistair Popple Cc: Arnaldo Carvalho de Melo Cc: Ian Rogers Cc: Ingo Molnar Cc: Jiri Olsa Cc: Kan Liang Cc: Marc Rutland Cc: "Masami Hiramatsu (Google)" Cc: Matthew Wilcox (Oracle) Cc: Namhyung kim Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Steven Rostedt Signed-off-by: Andrew Morton

mm/memfd: clarify error handling labels in memfd_create()

2025-07-10T05:42:05+00:00

err_name --> err_free_name (fd failure case) err_fd --> err_free_fd (file failure case) Link: https://lkml.kernel.org/r/20250610083730.527619-1-ye.liu@linux.dev Signed-off-by: Ye Liu Signed-off-by: Andrew Morton

mm: move folio_index to mm/swap.h and remove no longer needed helper

2025-05-13T06:50:50+00:00

There are no remaining users of folio_index() outside the mm subsystem. Move it to mm/swap.h to co-locate it with swap_cache_index(), eliminating a forward declaration, and a function call overhead. Also remove the helper that was used to fix circular header dependency issue. Link: https://lkml.kernel.org/r/20250430181052.55698-6-ryncsn@gmail.com Signed-off-by: Kairui Song Acked-by: David Hildenbrand Cc: Chao Yu Cc: Chris Li Cc: Chris Mason Cc: Christian Brauner Cc: David Sterba Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Jaegeuk Kim Cc: Joanne Koong Cc: Johannes Weiner Cc: Josef Bacik Cc: Matthew Wilcox (Oracle) Cc: Miklos Szeredi Cc: Nhat Pham Cc: Qu Wenruo Cc: Yosry Ahmed Signed-off-by: Andrew Morton

mm/memfd: fix spelling and grammatical issues

2025-03-17T05:06:04+00:00

The comment "If a private mapping then writability is irrelevant" contains a typo. It should be "If a private mapping then writability is irrelevant". The comment "SEAL_EXEC implys SEAL_WRITE, making W^X from the start." contains a typo. It should be "SEAL_EXEC implies SEAL_WRITE, making W^X from the start." Link: https://lkml.kernel.org/r/20250206060958.98010-1-liuye@kylinos.cn Signed-off-by: Liu Ye Signed-off-by: Andrew Morton

mm/memfd: use strncpy_from_user() to read memfd name

2025-01-26T04:22:40+00:00

The existing logic uses strnlen_user() to calculate the length of the memfd name from userspace and then copies the string into a buffer using copy_from_user(). This is error-prone, as the string length could have changed between the time when it was calculated and when the string was copied. The existing logic handles this by ensuring that the last byte in the buffer is the terminating zero. This handling is contrived and can better be handled by using strncpy_from_user(), which gets the length of the string and copies it in one shot. Therefore, simplify the logic for copying the memfd name by using strncpy_from_user(). No functional change. Link: https://lkml.kernel.org/r/20250110165904.3437374-3-isaacmanjarres@google.com Signed-off-by: Isaac J. Manjarres Reviewed-by: Alice Ryhl Reviewed-by: Lorenzo Stoakes Cc: John Stultz Cc: Kalesh Singh Cc: Suren Baghdasaryan Signed-off-by: Andrew Morton