From 644ad84870ab503f5619d21cf3d37efb134e82de Mon Sep 17 00:00:00 2001 From: Hajime Tazaki Date: Thu, 2 Jul 2026 10:25:46 +0900 Subject: [PATCH] mm: nommu: point to the write iterator upon split_vma When a user invokes munmap(2) on a partial region allocated by mmap(), the kernel may split the original region if necessary and shrink it to the correct size. At the beginning of vmi_shrink_vma(), the unused part is cleared; however, an assertion is triggered if the shrink occurs after split_vma(). This commit fixes the issue by correctly configuring the pointer to the iterator at the end of split_vma(). This bug was detected using the Linux Test Project (LTP) test linked below, running on a nommu UML (User-Mode Linux) environment (via an out-of-tree extension to UML). Here is a minimal reproducible chunk of code for this issue: void *addr; size_t pagesize = getpagesize(); addr = mmap(NULL, pagesize * 4, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); munmap(addr + pagesize * 1, pagesize); This is the console output with CONFIG_DEBUG_MAPLE_TREE=y. nommu: WARN at __mas_set_range:791 (1) MAS: tree=0000000091c23b08 enode=0000000065057663 (ma_active) Store Type: node_store [9/9] index=70af8000 last=ffffffffffffffff min=0 max=ffffffffffffffff sheaf=0000000000000000, request 0 depth=0, flags=0 maple_tree(0000000091c23b08) flags 307, height 1 root 0000000083394c06 0-ffffffffffffffff: node 0000000010c90bd6 depth 0 type 1 parent 0000000050e1ddf8 contents: 0000000000000000 707A 7FFF 00000000eb0ac2b5 707AFFFF 0000000000000000 7093FFFF 0000000045ead616 7095FFFF 0000000000000000 7096CFFF 000 00000681c7151 7096FFFF 0000000000000000 70AF3FFF 000000006c78b9e9 70AF4FFF 000000001914ab0b 70AF7FFF 00000000000 00000 FFFFFFFFFFFFFFFF 0000000000000000 0 0000000000000000 0 0000000000000000 0 0000000000000000 0 0000000000000 000 0 00000000bca8be4f 0-707a7fff: 0000000000000000 707a8000-707affff: 00000000eb0ac2b5 707b0000-7093ffff: 0000000000000000 70940000-7095ffff: 0000000045ead616 70960000-7096cfff: 0000000000000000 7096d000-7096ffff: 00000000681c7151 70970000-70af3fff: 0000000000000000 70af4000-70af4fff: 000000006c78b9e9 70af5000-70af7fff: 000000001914ab0b 70af8000-ffffffffffffffff: 0000000000000000 nommu: Pass: 796 Run:797 Link: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/mseal/mseal02.c Link: https://lore.kernel.org/20260702012546.665383-1-thehajime@gmail.com Signed-off-by: Hajime Tazaki Cc: Jann Horn Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Pedro Falcato Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- mm/nommu.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/nommu.c b/mm/nommu.c index 277f663e1c5b..498e01ee40b0 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1393,6 +1393,10 @@ static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, setup_vma_to_mm(vma, mm); setup_vma_to_mm(new, mm); vma_iter_store_new(vmi, new); + + /* vmi should point lower address */ + if (new_below) + vma_next(vmi); mm->map_count++; return 0;