Message-ID: <402e154c-9aad-4644-ac72-fdb94f0aa66f@lucifer.local>
Date: Sat, 16 Aug 2025 08:32:51 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: syzbot <syzbot+4e221abf50259362f4f4@...kaller.appspotmail.com>
Cc: Liam.Howlett@...cle.com, akpm@...ux-foundation.org, jannh@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, pfalcato@...e.de,
        syzkaller-bugs@...glegroups.com, vbabka@...e.cz
Subject: Re: [syzbot] [mm?] KASAN: slab-use-after-free Read in mremap

On Fri, Aug 15, 2025 at 08:07:34PM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    931e46dcbc7e Add linux-next specific files for 20250814
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=16a66af0580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=bb7fbecfa2364d1c
> dashboard link: https://syzkaller.appspot.com/bug?extid=4e221abf50259362f4f4
> 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=11fb3c34580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=173c2dbc580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/68e3ffeee4c1/disk-931e46dc.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/3cc40de4a0c3/vmlinux-931e46dc.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/aed3e4f6a518/bzImage-931e46dc.xz
>
> The issue was bisected to:
>
> commit d50dabff4d1f2c815b2faf184f5d6db40596e2cc
> Author: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Date:   Sun Aug 3 11:11:22 2025 +0000
>
>     mm/mremap: catch invalid multi VMA moves earlier

Thanks for report.

>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16fadda2580000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=15fadda2580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=11fadda2580000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+4e221abf50259362f4f4@...kaller.appspotmail.com
> Fixes: d50dabff4d1f ("mm/mremap: catch invalid multi VMA moves earlier")
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in vma_multi_allowed mm/mremap.c:1623 [inline]
> BUG: KASAN: slab-use-after-free in remap_move mm/mremap.c:1884 [inline]
> BUG: KASAN: slab-use-after-free in do_mremap mm/mremap.c:1923 [inline]
> BUG: KASAN: slab-use-after-free in __do_sys_mremap mm/mremap.c:1987 [inline]
> BUG: KASAN: slab-use-after-free in __se_sys_mremap+0xb33/0x1150 mm/mremap.c:1955
> Read of size 8 at addr ffff888074738558 by task syz.0.59/6077
>
> CPU: 1 UID: 0 PID: 6077 Comm: syz.0.59 Not tainted 6.17.0-rc1-next-20250814-syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
> 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/0x240 mm/kasan/report.c:482
>  kasan_report+0x118/0x150 mm/kasan/report.c:595
>  vma_multi_allowed mm/mremap.c:1623 [inline]

OK this is a pretty easy one, we're reusing a VMA after we may merge/do
something else with it, silly mistake because of rearranging things around a
bit, will send a hotfix.

>  remap_move mm/mremap.c:1884 [inline]
>  do_mremap mm/mremap.c:1923 [inline]
>  __do_sys_mremap mm/mremap.c:1987 [inline]
>  __se_sys_mremap+0xb33/0x1150 mm/mremap.c:1955
>  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: 0033:0x7f7fd678ebe9
> 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:00007fff51cbeae8 EFLAGS: 00000246 ORIG_RAX: 0000000000000019
> RAX: ffffffffffffffda RBX: 00007f7fd69b5fa0 RCX: 00007f7fd678ebe9
> RDX: 0000000000002000 RSI: 0000000000002000 RDI: 0000200000041000
> RBP: 00007f7fd6811e19 R08: 00002000004c3000 R09: 0000000000000000
> R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f7fd69b5fa0 R14: 00007f7fd69b5fa0 R15: 0000000000000005
>  </TASK>
>
> Allocated by task 5972:
>  kasan_save_stack mm/kasan/common.c:56 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
>  unpoison_slab_object mm/kasan/common.c:339 [inline]
>  __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:365
>  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
>  vm_area_dup+0x2b/0x680 mm/vma_init.c:122
>  dup_mmap+0x90c/0x1ac0 mm/mmap.c:1780
>  dup_mm kernel/fork.c:1485 [inline]
>  copy_mm+0x13c/0x4b0 kernel/fork.c:1537
>  copy_process+0x1706/0x3c00 kernel/fork.c:2175
>  kernel_clone+0x21e/0x840 kernel/fork.c:2605
>  __do_sys_clone kernel/fork.c:2748 [inline]
>  __se_sys_clone kernel/fork.c:2732 [inline]
>  __x64_sys_clone+0x18b/0x1e0 kernel/fork.c:2732
>  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 2999:
>  kasan_save_stack mm/kasan/common.c:56 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
>  __kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:587
>  kasan_save_free_info mm/kasan/kasan.h:406 [inline]
>  poison_slab_object mm/kasan/common.c:252 [inline]
>  __kasan_slab_free+0x5b/0x80 mm/kasan/common.c:284
>  kasan_slab_free include/linux/kasan.h:233 [inline]
>  slab_free_hook mm/slub.c:2417 [inline]
>  slab_free_after_rcu_debug+0x129/0x2a0 mm/slub.c:4730
>  rcu_do_batch kernel/rcu/tree.c:2605 [inline]
>  rcu_core+0xca8/0x1770 kernel/rcu/tree.c:2861
>  handle_softirqs+0x286/0x870 kernel/softirq.c:579
>  do_softirq+0xec/0x180 kernel/softirq.c:480
>  __local_bh_enable_ip+0x17d/0x1c0 kernel/softirq.c:407
>  spin_unlock_bh include/linux/spinlock.h:396 [inline]
>  batadv_nc_purge_paths+0x318/0x3b0 net/batman-adv/network-coding.c:471
>  batadv_nc_worker+0x328/0x610 net/batman-adv/network-coding.c:720
>  process_one_work kernel/workqueue.c:3236 [inline]
>  process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
>  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
>  kthread+0x711/0x8a0 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:56
>  kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:559
>  slab_free_hook mm/slub.c:2378 [inline]
>  slab_free mm/slub.c:4680 [inline]
>  kmem_cache_free+0x2f6/0x400 mm/slub.c:4782
>  remove_vma mm/vma.c:468 [inline]
>  vms_complete_munmap_vmas+0x626/0x8a0 mm/vma.c:1293
>  do_vmi_align_munmap+0x358/0x420 mm/vma.c:1536
>  do_vmi_munmap+0x253/0x2e0 mm/vma.c:1584
>  do_munmap+0xe1/0x140 mm/mmap.c:1068
>  mremap_to+0x2df/0x7a0 mm/mremap.c:1372
>  remap_move mm/mremap.c:1879 [inline]
>  do_mremap mm/mremap.c:1923 [inline]
>  __do_sys_mremap mm/mremap.c:1987 [inline]
>  __se_sys_mremap+0xadf/0x1150 mm/mremap.c:1955
>  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 ffff888074738500
>  which belongs to the cache vm_area_struct of size 256
> The buggy address is located 88 bytes inside of
>  freed 256-byte region [ffff888074738500, ffff888074738600)
>
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x74738
> memcg:ffff888030d7f981
> flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
> page_type: f5(slab)
> raw: 00fff00000000000 ffff88801bed5b40 dead000000000100 dead000000000122
> raw: 0000000000000000 00000000000c000c 00000000f5000000 ffff888030d7f981
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Unmovable, gfp_mask 0x52cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 5248, tgid 5248 (udevd), ts 24347982328, free_ts 24338159697
>  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
>  vm_area_dup+0x2b/0x680 mm/vma_init.c:122
>  dup_mmap+0x90c/0x1ac0 mm/mmap.c:1780
>  dup_mm kernel/fork.c:1485 [inline]
>  copy_mm+0x13c/0x4b0 kernel/fork.c:1537
>  copy_process+0x1706/0x3c00 kernel/fork.c:2175
>  kernel_clone+0x21e/0x840 kernel/fork.c:2605
>  __do_sys_clone kernel/fork.c:2748 [inline]
>  __se_sys_clone kernel/fork.c:2732 [inline]
>  __x64_sys_clone+0x18b/0x1e0 kernel/fork.c:2732
>  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
> page last free pid 23 tgid 23 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
>  pagetable_free include/linux/mm.h:2917 [inline]
>  pagetable_dtor_free include/linux/mm.h:3015 [inline]
>  __tlb_remove_table+0x2d2/0x3b0 include/asm-generic/tlb.h:220
>  __tlb_remove_table_free mm/mmu_gather.c:227 [inline]
>  tlb_remove_table_rcu+0x85/0x100 mm/mmu_gather.c:290
>  rcu_do_batch kernel/rcu/tree.c:2605 [inline]
>  rcu_core+0xca8/0x1770 kernel/rcu/tree.c:2861
>  handle_softirqs+0x286/0x870 kernel/softirq.c:579
>  run_ksoftirqd+0x9b/0x100 kernel/softirq.c:968
>  smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
>  kthread+0x711/0x8a0 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
>
> Memory state around the buggy address:
>  ffff888074738400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888074738480: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> >ffff888074738500: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                     ^
>  ffff888074738580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888074738600: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup

Powered by blists - more mailing lists