Re: [syzbot] [mm?] KASAN: slab-use-after-free Read in madvise_collapse

[Hugh Dickins]

On Sun, 23 Jul 2023, syzbot wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    ae867bc97b71 Add linux-next specific files for 20230721
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1553a881a80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c403a6b36e7c85ac
> dashboard link: https://syzkaller.appspot.com/bug?extid=173cc8cfdfbbef6dd755
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1076d84aa80000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=161debd1a80000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/a76b93f21f84/disk-ae867bc9.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/8eb30097a952/vmlinux-ae867bc9.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/7506a6b3ec38/bzImage-ae867bc9.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+173cc8cfdfbbef6dd755@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ==================================================================
> BUG: KASAN: slab-use-after-free in madvise_collapse+0xa6c/0xb50 mm/khugepaged.c:2723
> Read of size 8 at addr ffff88802b4e6588 by task syz-executor296/5046
> 
> CPU: 0 PID: 5046 Comm: syz-executor296 Not tainted 6.5.0-rc2-next-20230721-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2023
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
>  print_address_description mm/kasan/report.c:364 [inline]
>  print_report+0xc4/0x620 mm/kasan/report.c:475
>  kasan_report+0xda/0x110 mm/kasan/report.c:588
>  madvise_collapse+0xa6c/0xb50 mm/khugepaged.c:2723
>  madvise_vma_behavior+0x200/0x1e60 mm/madvise.c:1094
>  madvise_walk_vmas+0x1cf/0x2c0 mm/madvise.c:1268
>  do_madvise+0x333/0x660 mm/madvise.c:1448
>  __do_sys_madvise mm/madvise.c:1461 [inline]
>  __se_sys_madvise mm/madvise.c:1459 [inline]
>  __x64_sys_madvise+0xaa/0x110 mm/madvise.c:1459
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f7ec298d359
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f7ec292d238 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
> RAX: ffffffffffffffda RBX: 00007f7ec2a17318 RCX: 00007f7ec298d359
> RDX: 0000000000000019 RSI: 000000000060005f RDI: 0000000020000000
> RBP: 00007f7ec2a17310 R08: 00007fffd329edf7 R09: 00007f7ec292d6c0
> R10: 0000000000000000 R11: 0000000000000246 R12: b635773f07ebbeea
> R13: 000000000000006e R14: 00007fffd329ed10 R15: 00007fffd329edf8
>  </TASK>
> 
> Allocated by task 5033:
>  kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
>  kasan_set_track+0x25/0x30 mm/kasan/common.c:52
>  __kasan_slab_alloc+0x81/0x90 mm/kasan/common.c:328
>  kasan_slab_alloc include/linux/kasan.h:186 [inline]
>  slab_post_alloc_hook mm/slab.h:762 [inline]
>  slab_alloc_node mm/slub.c:3478 [inline]
>  slab_alloc mm/slub.c:3486 [inline]
>  __kmem_cache_alloc_lru mm/slub.c:3493 [inline]
>  kmem_cache_alloc+0x172/0x3b0 mm/slub.c:3502
>  vm_area_alloc+0x1f/0x220 kernel/fork.c:485
>  mmap_region+0x386/0x2640 mm/mmap.c:2717
>  do_mmap+0x87c/0xed0 mm/mmap.c:1353
>  vm_mmap_pgoff+0x1a6/0x3b0 mm/util.c:543
>  ksys_mmap_pgoff+0x7d/0x5b0 mm/mmap.c:1399
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Freed by task 5035:
>  kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
>  kasan_set_track+0x25/0x30 mm/kasan/common.c:52
>  kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:522
>  ____kasan_slab_free mm/kasan/common.c:236 [inline]
>  ____kasan_slab_free+0x15e/0x1b0 mm/kasan/common.c:200
>  kasan_slab_free include/linux/kasan.h:162 [inline]
>  slab_free_hook mm/slub.c:1800 [inline]
>  slab_free_freelist_hook+0x114/0x1e0 mm/slub.c:1826
>  slab_free mm/slub.c:3809 [inline]
>  kmem_cache_free+0xf0/0x490 mm/slub.c:3831
>  rcu_do_batch kernel/rcu/tree.c:2139 [inline]
>  rcu_core+0x7fb/0x1bb0 kernel/rcu/tree.c:2403
>  __do_softirq+0x218/0x965 kernel/softirq.c:553
> 
> Last potentially related work creation:
>  kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
>  __kasan_record_aux_stack+0xbc/0xd0 mm/kasan/generic.c:492
>  __call_rcu_common.constprop.0+0x9a/0x790 kernel/rcu/tree.c:2653
>  remove_vma+0x140/0x170 mm/mmap.c:148
>  remove_mt mm/mmap.c:2285 [inline]
>  do_vmi_align_munmap+0xf75/0x1710 mm/mmap.c:2547
>  do_vmi_munmap+0x20e/0x450 mm/mmap.c:2611
>  mmap_region+0x194/0x2640 mm/mmap.c:2661
>  do_mmap+0x87c/0xed0 mm/mmap.c:1353
>  vm_mmap_pgoff+0x1a6/0x3b0 mm/util.c:543
>  ksys_mmap_pgoff+0x7d/0x5b0 mm/mmap.c:1399
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> The buggy address belongs to the object at ffff88802b4e6500
>  which belongs to the cache vm_area_struct of size 192
> The buggy address is located 136 bytes inside of
>  freed 192-byte region [ffff88802b4e6500, ffff88802b4e65c0)
> 
> The buggy address belongs to the physical page:
> page:ffffea0000ad3980 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2b4e6
> flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
> page_type: 0xffffffff()
> raw: 00fff00000000200 ffff888014674b40 ffffea0001dce680 dead000000000002
> raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 4724, tgid 4724 (dhcpcd-run-hook), ts 33134643925, free_ts 33125953991
>  set_page_owner include/linux/page_owner.h:31 [inline]
>  post_alloc_hook+0x2d2/0x350 mm/page_alloc.c:1569
>  prep_new_page mm/page_alloc.c:1576 [inline]
>  get_page_from_freelist+0x10d7/0x31b0 mm/page_alloc.c:3256
>  __alloc_pages+0x1d0/0x4a0 mm/page_alloc.c:4512
>  alloc_pages+0x1a9/0x270 mm/mempolicy.c:2279
>  alloc_slab_page mm/slub.c:1870 [inline]
>  allocate_slab+0x24e/0x380 mm/slub.c:2017
>  new_slab mm/slub.c:2070 [inline]
>  ___slab_alloc+0x8bc/0x1570 mm/slub.c:3223
>  __slab_alloc.constprop.0+0x56/0xa0 mm/slub.c:3322
>  __slab_alloc_node mm/slub.c:3375 [inline]
>  slab_alloc_node mm/slub.c:3468 [inline]
>  slab_alloc mm/slub.c:3486 [inline]
>  __kmem_cache_alloc_lru mm/slub.c:3493 [inline]
>  kmem_cache_alloc+0x392/0x3b0 mm/slub.c:3502
>  vm_area_alloc+0x1f/0x220 kernel/fork.c:485
>  mmap_region+0x386/0x2640 mm/mmap.c:2717
>  do_mmap+0x87c/0xed0 mm/mmap.c:1353
>  vm_mmap_pgoff+0x1a6/0x3b0 mm/util.c:543
>  ksys_mmap_pgoff+0x422/0x5b0 mm/mmap.c:1399
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> page last free stack trace:
>  reset_page_owner include/linux/page_owner.h:24 [inline]
>  free_pages_prepare mm/page_alloc.c:1160 [inline]
>  free_unref_page_prepare+0x508/0xb90 mm/page_alloc.c:2383
>  free_unref_page+0x33/0x3b0 mm/page_alloc.c:2478
>  vfree+0x181/0x7a0 mm/vmalloc.c:2842
>  delayed_vfree_work+0x56/0x70 mm/vmalloc.c:2763
>  process_one_work+0xaa2/0x16f0 kernel/workqueue.c:2600
>  worker_thread+0x687/0x1110 kernel/workqueue.c:2751
>  kthread+0x33a/0x430 kernel/kthread.c:389
>  ret_from_fork+0x2c/0x70 arch/x86/kernel/process.c:145
>  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:296
> 
> Memory state around the buggy address:
>  ffff88802b4e6480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>  ffff88802b4e6500: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff88802b4e6580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>                       ^
>  ffff88802b4e6600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffff88802b4e6680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
> ==================================================================

I don't think we need to worry about this report: it should be fixed by
https://lore.kernel.org/linux-mm/b53be6a4-7715-51f9-aad-f1347dcb7c4@xxxxxxxxxx/T/#m9e27b97ad27df2551ec54ef220417c1aa263b161

Hugh