6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kairui Song kasong@tencent.com
commit fc745ff317566ec299e16346ebb9eacc8fe5b9d2 upstream.
The order check and fallback loop is updating the index value on every loop. This will cause the index to be wrongly aligned by a larger value while the loop shrinks the order.
This may result in inserting and returning a folio of the wrong index and cause data corruption with some userspace workloads [1].
[kasong@tencent.com: introduce a temporary variable to improve code] Link: https://lkml.kernel.org/r/20251023065913.36925-1-ryncsn@gmail.com Link: https://lore.kernel.org/linux-mm/CAMgjq7DqgAmj25nDUwwu1U2cSGSn8n4-Hqpgottedy... [1] Link: https://lkml.kernel.org/r/20251022105719.18321-1-ryncsn@gmail.com Link: https://lore.kernel.org/linux-mm/CAMgjq7DqgAmj25nDUwwu1U2cSGSn8n4-Hqpgottedy... [1] Fixes: e7a2ab7b3bb5 ("mm: shmem: add mTHP support for anonymous shmem") Closes: https://lore.kernel.org/linux-mm/CAMgjq7DqgAmj25nDUwwu1U2cSGSn8n4-Hqpgottedy... Signed-off-by: Kairui Song kasong@tencent.com Acked-by: David Hildenbrand david@redhat.com Acked-by: Zi Yan ziy@nvidia.com Reviewed-by: Baolin Wang baolin.wang@linux.alibaba.com Reviewed-by: Barry Song baohua@kernel.org Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Dev Jain dev.jain@arm.com Cc: Hugh Dickins hughd@google.com Cc: Liam Howlett liam.howlett@oracle.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Nico Pache npache@redhat.com Cc: Ryan Roberts ryan.roberts@arm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/shmem.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
--- a/mm/shmem.c +++ b/mm/shmem.c @@ -1785,6 +1785,7 @@ static struct folio *shmem_alloc_and_add struct shmem_inode_info *info = SHMEM_I(inode); unsigned long suitable_orders = 0; struct folio *folio = NULL; + pgoff_t aligned_index; long pages; int error, order;
@@ -1798,10 +1799,12 @@ static struct folio *shmem_alloc_and_add order = highest_order(suitable_orders); while (suitable_orders) { pages = 1UL << order; - index = round_down(index, pages); - folio = shmem_alloc_folio(gfp, order, info, index); - if (folio) + aligned_index = round_down(index, pages); + folio = shmem_alloc_folio(gfp, order, info, aligned_index); + if (folio) { + index = aligned_index; goto allocated; + }
if (pages == HPAGE_PMD_NR) count_vm_event(THP_FILE_FALLBACK);