From: Xiangfeng Cai Date: Mon, 13 Jul 2026 17:14:55 +0000 (+0800) Subject: mm/hugetlb: fix list corruption in allocate_file_region_entries() X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=dd9623f58ec702a07b2d67179d6fcea79c52231a;p=thirdparty%2Fkernel%2Flinux.git mm/hugetlb: fix list corruption in allocate_file_region_entries() allocate_file_region_entries() tops up resv->region_cache with freshly allocated file_region descriptors. The allocation uses GFP_KERNEL, so resv->lock is dropped around it: the new entries are gathered on a stack-local list head, allocated_regions, and spliced into resv->region_cache once the lock is re-acquired. The splice used list_splice(), which moves the entries but does not re-initialize the source head, so allocated_regions is left pointing at an entry that now lives on resv->region_cache. The top-up runs in a while loop that re-checks the cache deficit after re-acquiring the lock. For a shared mapping the resv_map is shared by every mapper of the hugetlbfs inode, so a concurrent region_chg()/region_add()/region_del() on the same resv_map can consume cache entries during the unlocked window and force a second iteration. That iteration calls list_add() on the stale head and corrupts the list; with CONFIG_DEBUG_LIST the __list_add_valid() check trips: list_add corruption. next->prev should be prev (ffffc900011ff7f8), but was ffff88814c281460. (next=ffff88814c545640). kernel BUG at lib/list_debug.c:31! allocate_file_region_entries+0x191/0x420 region_chg+0x267/0x300 hugetlb_reserve_pages+0x387/0xc80 hugetlbfs_file_mmap+0x2ce/0x3f0 mmap_region+0x1348/0x1a80 do_mmap+0x85e/0xb90 vm_mmap_pgoff+0x18c/0x330 ksys_mmap_pgoff+0x2a1/0x3e0 do_syscall_64+0xd7/0x420 Without CONFIG_DEBUG_LIST the bad list_add() silently links a kernel-stack address into resv->region_cache, leading to later use-after-free. This was observed as a real host panic on a dense KVM host where a QEMU guest-RAM hugetlbfs file was mapped MAP_SHARED by both QEMU and a separate SPDK/DPDK vhost-user target, generating concurrent region_* traffic on one shared resv_map. Use list_splice_init() so the source head is re-initialized empty after each splice, making the retry loop safe. Link: https://lore.kernel.org/20260713171456.300518-2-caixiangfeng@bytedance.com Fixes: d3ec7b6e09e5 ("mm/hugetlb: use list_splice to merge two list at once") Signed-off-by: Xiangfeng Cai Reviewed-by: Muchun Song Cc: Baoquan He Cc: David Hildenbrand Cc: Oscar Salvador Cc: Shuah Khan Cc: Wei Yang Cc: Signed-off-by: Andrew Morton --- diff --git a/mm/hugetlb.c b/mm/hugetlb.c index bca2707d02e3..e93c4d2456aa 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -693,7 +693,7 @@ static int allocate_file_region_entries(struct resv_map *resv, spin_lock(&resv->lock); - list_splice(&allocated_regions, &resv->region_cache); + list_splice_init(&allocated_regions, &resv->region_cache); resv->region_cache_count += to_allocate; }