Re: [syzbot] [mm?] KASAN: slab-use-after-free Read in mas_next_slot (2)

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

Thanks for the report.

This is due to an older version of the series being in -next which allowed
MREMAP_DONTUNMAP for the move operation which was incorrect.

Andrew - I guess you will merge the newer version to linux-next soon?

In any event, this report is therefore bogus.

Cheers, Lorenzo

On Wed, Jul 16, 2025 at 10:55:35AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    0be23810e32e Add linux-next specific files for 20250714
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=11a9a7d4580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=adc3ea2bfe31343b
> dashboard link: https://syzkaller.appspot.com/bug?extid=ebfd0e44b5c11034e1eb
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11d0658c580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15dd858c580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/13b5be5048fe/disk-0be23810.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/3d2b3b2ceddf/vmlinux-0be23810.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/c7e5fbf3efa6/bzImage-0be23810.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+ebfd0e44b5c11034e1eb@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in ma_dead_node lib/maple_tree.c:575 [inline]
> BUG: KASAN: slab-use-after-free in mas_rewalk_if_dead lib/maple_tree.c:4415 [inline]
> BUG: KASAN: slab-use-after-free in mas_next_slot+0x185/0xcf0 lib/maple_tree.c:4697
> Read of size 8 at addr ffff8880755dc600 by task syz.0.656/6830
>
> CPU: 1 UID: 0 PID: 6830 Comm: syz.0.656 Not tainted 6.16.0-rc6-next-20250714-syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>  print_address_description mm/kasan/report.c:378 [inline]
>  print_report+0xca/0x230 mm/kasan/report.c:480
>  kasan_report+0x118/0x150 mm/kasan/report.c:593
>  ma_dead_node lib/maple_tree.c:575 [inline]
>  mas_rewalk_if_dead lib/maple_tree.c:4415 [inline]
>  mas_next_slot+0x185/0xcf0 lib/maple_tree.c:4697
>  mas_find+0xb0e/0xd30 lib/maple_tree.c:6062
>  vma_find include/linux/mm.h:855 [inline]
>  remap_move mm/mremap.c:1819 [inline]
>  do_mremap mm/mremap.c:1904 [inline]
>  __do_sys_mremap mm/mremap.c:1968 [inline]
>  __se_sys_mremap+0xaff/0xef0 mm/mremap.c:1936
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f4fecf8e929
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fff93ea4718 EFLAGS: 00000246 ORIG_RAX: 0000000000000019
> RAX: ffffffffffffffda RBX: 00007f4fed1b5fa0 RCX: 00007f4fecf8e929
> RDX: 0000000000600002 RSI: 0000000000600002 RDI: 0000200000000000
> RBP: 00007f4fed010b39 R08: 0000200000a00000 R09: 0000000000000000
> R10: 0000000000000007 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f4fed1b5fa0 R14: 00007f4fed1b5fa0 R15: 0000000000000005
>  </TASK>
>
> Allocated by task 6830:
>  kasan_save_stack mm/kasan/common.c:47 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
>  unpoison_slab_object mm/kasan/common.c:319 [inline]
>  __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:345
>  kasan_slab_alloc include/linux/kasan.h:250 [inline]
>  slab_post_alloc_hook mm/slub.c:4180 [inline]
>  slab_alloc_node mm/slub.c:4229 [inline]
>  kmem_cache_alloc_noprof+0x1c1/0x3c0 mm/slub.c:4236
>  mt_alloc_one lib/maple_tree.c:176 [inline]
>  mas_alloc_nodes+0x2e9/0x8e0 lib/maple_tree.c:1255
>  mas_node_count_gfp lib/maple_tree.c:1337 [inline]
>  mas_preallocate+0x3ad/0x6f0 lib/maple_tree.c:5537
>  vma_iter_prealloc mm/vma.h:463 [inline]
>  __split_vma+0x2fa/0xa00 mm/vma.c:528
>  vms_gather_munmap_vmas+0x2de/0x12b0 mm/vma.c:1359
>  __mmap_prepare mm/vma.c:2361 [inline]
>  __mmap_region mm/vma.c:2653 [inline]
>  mmap_region+0x724/0x20c0 mm/vma.c:2741
>  do_mmap+0xc45/0x10d0 mm/mmap.c:561
>  vm_mmap_pgoff+0x2a6/0x4d0 mm/util.c:579
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Freed by task 23:
>  kasan_save_stack mm/kasan/common.c:47 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
>  kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
>  poison_slab_object mm/kasan/common.c:247 [inline]
>  __kasan_slab_free+0x62/0x70 mm/kasan/common.c:264
>  kasan_slab_free include/linux/kasan.h:233 [inline]
>  slab_free_hook mm/slub.c:2417 [inline]
>  slab_free mm/slub.c:4680 [inline]
>  kmem_cache_free+0x18f/0x400 mm/slub.c:4782
>  rcu_do_batch kernel/rcu/tree.c:2584 [inline]
>  rcu_core+0xca8/0x1710 kernel/rcu/tree.c:2840
>  handle_softirqs+0x283/0x870 kernel/softirq.c:579
>  run_ksoftirqd+0x9b/0x100 kernel/softirq.c:968
>  smpboot_thread_fn+0x53f/0xa60 kernel/smpboot.c:160
>  kthread+0x70e/0x8a0 kernel/kthread.c:463
>  ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>
> Last potentially related work creation:
>  kasan_save_stack+0x3e/0x60 mm/kasan/common.c:47
>  kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:548
>  __call_rcu_common kernel/rcu/tree.c:3102 [inline]
>  call_rcu+0x157/0x9c0 kernel/rcu/tree.c:3222
>  mas_wr_node_store lib/maple_tree.c:3893 [inline]
>  mas_wr_store_entry+0x1f1b/0x25b0 lib/maple_tree.c:4104
>  mas_store_prealloc+0xb00/0xf60 lib/maple_tree.c:5510
>  vma_iter_store_new mm/vma.h:509 [inline]
>  vma_complete+0x224/0xae0 mm/vma.c:354
>  __split_vma+0x8a6/0xa00 mm/vma.c:568
>  vms_gather_munmap_vmas+0x2de/0x12b0 mm/vma.c:1359
>  do_vmi_align_munmap+0x25d/0x420 mm/vma.c:1527
>  do_vmi_munmap+0x253/0x2e0 mm/vma.c:1584
>  do_munmap+0xe1/0x140 mm/mmap.c:1071
>  mremap_to+0x304/0x7b0 mm/mremap.c:1367
>  remap_move mm/mremap.c:1861 [inline]
>  do_mremap mm/mremap.c:1904 [inline]
>  __do_sys_mremap mm/mremap.c:1968 [inline]
>  __se_sys_mremap+0xa0b/0xef0 mm/mremap.c:1936
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> The buggy address belongs to the object at ffff8880755dc600
>  which belongs to the cache maple_node of size 256
> The buggy address is located 0 bytes inside of
>  freed 256-byte region [ffff8880755dc600, ffff8880755dc700)
>
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x755dc
> head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
> page_type: f5(slab)
> raw: 00fff00000000040 ffff88801a491000 dead000000000122 0000000000000000
> raw: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
> head: 00fff00000000040 ffff88801a491000 dead000000000122 0000000000000000
> head: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
> head: 00fff00000000001 ffffea0001d57701 00000000ffffffff 00000000ffffffff
> head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000002
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 6828, tgid 6828 (cmp), ts 120765032919, free_ts 112542256570
>  set_page_owner include/linux/page_owner.h:32 [inline]
>  post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
>  prep_new_page mm/page_alloc.c:1859 [inline]
>  get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3858
>  __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
>  alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
>  alloc_slab_page mm/slub.c:2487 [inline]
>  allocate_slab+0x8a/0x370 mm/slub.c:2655
>  new_slab mm/slub.c:2709 [inline]
>  ___slab_alloc+0xbeb/0x1410 mm/slub.c:3891
>  __slab_alloc mm/slub.c:3981 [inline]
>  __slab_alloc_node mm/slub.c:4056 [inline]
>  slab_alloc_node mm/slub.c:4217 [inline]
>  kmem_cache_alloc_noprof+0x283/0x3c0 mm/slub.c:4236
>  mt_alloc_one lib/maple_tree.c:176 [inline]
>  mas_alloc_nodes+0x2e9/0x8e0 lib/maple_tree.c:1255
>  mas_node_count_gfp lib/maple_tree.c:1337 [inline]
>  mas_preallocate+0x3ad/0x6f0 lib/maple_tree.c:5537
>  vma_iter_prealloc mm/vma.h:463 [inline]
>  commit_merge+0x1fd/0x700 mm/vma.c:753
>  vma_expand+0x40c/0x7e0 mm/vma.c:1158
>  vma_merge_new_range+0x6a3/0x860 mm/vma.c:1095
>  __mmap_region mm/vma.c:2666 [inline]
>  mmap_region+0xd46/0x20c0 mm/vma.c:2741
>  do_mmap+0xc45/0x10d0 mm/mmap.c:561
>  vm_mmap_pgoff+0x2a6/0x4d0 mm/util.c:579
>  ksys_mmap_pgoff+0x51f/0x760 mm/mmap.c:607
> page last free pid 5955 tgid 5955 stack trace:
>  reset_page_owner include/linux/page_owner.h:25 [inline]
>  free_pages_prepare mm/page_alloc.c:1395 [inline]
>  __free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2895
>  __slab_free+0x303/0x3c0 mm/slub.c:4591
>  qlink_free mm/kasan/quarantine.c:163 [inline]
>  qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179
>  kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
>  __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:329
>  kasan_slab_alloc include/linux/kasan.h:250 [inline]
>  slab_post_alloc_hook mm/slub.c:4180 [inline]
>  slab_alloc_node mm/slub.c:4229 [inline]
>  kmem_cache_alloc_noprof+0x1c1/0x3c0 mm/slub.c:4236
>  getname_flags+0xb8/0x540 fs/namei.c:146
>  getname include/linux/fs.h:2914 [inline]
>  do_sys_openat2+0xbc/0x1c0 fs/open.c:1429
>  do_sys_open fs/open.c:1450 [inline]
>  __do_sys_openat fs/open.c:1466 [inline]
>  __se_sys_openat fs/open.c:1461 [inline]
>  __x64_sys_openat+0x138/0x170 fs/open.c:1461
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Memory state around the buggy address:
>  ffff8880755dc500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8880755dc580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >ffff8880755dc600: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                    ^
>  ffff8880755dc680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880755dc700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> ---
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