From 7a2e7ae5d13658ada38898e5a3a8a40a7910db06 Mon Sep 17 00:00:00 2001 From: Kemeng Shi Date: Sun, 23 Feb 2025 00:08:46 +0800 Subject: [PATCH] mm: swap: use correct step in loop to wait all clusters in wait_for_allocation() Use correct step in loop to wait all clusters in wait_for_allocation(). If we miss some cluster in wait_for_allocation(), use after free may occur as follows: shmem_writepage swapoff folio_alloc_swap get_swap_pages scan_swap_map_slots cluster_alloc_swap_entry alloc_swap_scan_cluster cluster_alloc_range /* SWP_WRITEOK is valid */ if (!(si->flags & SWP_WRITEOK)) ... del_from_avail_list(p, true); ... /* miss the cluster in shmem_writepage */ wait_for_allocation() ... try_to_unuse() memset(si->swap_map + start, usage, nr_pages); swap_range_alloc(si, nr_pages); ci->count += nr_pages; /* return a valid entry */ ... exit_swap_address_space(p->type); ... ... add_to_swap_cache /* dereference swap_address_space(entry) which is NULL */ xas_lock_irq(&xas); Link: https://lkml.kernel.org/r/20250222160850.505274-3-shikemeng@huaweicloud.com Fixes: 9a0ddeb79880 ("mm, swap: hold a reference during scan and cleanup flag usage") Signed-off-by: Kemeng Shi Reviewed-by: Kairui Song Signed-off-by: Andrew Morton --- mm/swapfile.c | 1 - 1 file changed, 1 deletion(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index a6c41c7ffb03..6460b6cb36c9 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -2645,7 +2645,6 @@ static void wait_for_allocation(struct swap_info_struct *si) for (offset = 0; offset < end; offset += SWAPFILE_CLUSTER) { ci = lock_cluster(si, offset); unlock_cluster(ci); - offset += SWAPFILE_CLUSTER; } } -- 2.49.0