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

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

On Thu, Mar 20, 2025 at 08:39:43PM +0100, Jann Horn wrote:
> +maintainers of Memory Mapping code
>
> I was looking around on lore and stumbled over this syzbot report from
> last month of an anon_vma UAF. I guess it kinda looks like we somehow
> ended up with a folio whose mapcount is >0 and whose ->mapping still
> points to an anon_vma that has already been freed?
>
> (Note that this was caught with participation of the
> slab_free_after_rcu_debug debugging mechanism that I introduced last
> year - which I guess means there is also a chance that this is a bug
> in the debugging mechanism. I don't think so, but I figured I should
> at least mention the possibility...)
>
> There was another bug report similar to this one a few days earlier,
> see <https://lore.kernel.org/all/67a76f33.050a0220.3d72c.0028.GAE@google.com/>.
>
> Syzkaller hasn't found any reproducer for this yet, likely because you
> only get a KASAN crash if the shrinker / compaction / ... happens to
> run at exactly the right time. Do any of you have a good idea of what
> bug this could be, or do we need to figure out some debug assertions
> we can sprinkle in the code so that syzkaller can find a more reliable
> reproducer in the future?

Thanks, how strange. Two in one evening like this :))

and I caught one like this in vma_modify() (but then broken another like unusual
case).

rmap locking (or lack thereof...) deeply concerns me.

I'll look into this in more depth when I have time, thanks!

>
> On Tue, Feb 11, 2025 at 9:10 PM syzbot
> <syzbot+402900951482ab0a6fcb@syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    bb066fe812d6 Merge tag 'pci-v6.14-fixes-2' of git://git.ke..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=170aa1b0580000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=c48f582603dcb16c
> > dashboard link: https://syzkaller.appspot.com/bug?extid=402900951482ab0a6fcb
> > compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/988222f4ae63/disk-bb066fe8.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/41a93a7bd0c9/vmlinux-bb066fe8.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/99bd53f622e1/bzImage-bb066fe8.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+402900951482ab0a6fcb@syzkaller.appspotmail.com
> >
> > ==================================================================
> > BUG: KASAN: slab-use-after-free in folio_lock_anon_vma_read+0xc4e/0xd40 mm/rmap.c:559
> > Read of size 8 at addr ffff888012dd7ee0 by task syz.0.7085/4643
> >
> > CPU: 1 UID: 0 PID: 4643 Comm: syz.0.7085 Not tainted 6.14.0-rc1-syzkaller-00081-gbb066fe812d6 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:94 [inline]
> >  dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
> >  print_address_description mm/kasan/report.c:378 [inline]
> >  print_report+0xc3/0x620 mm/kasan/report.c:489
> >  kasan_report+0xd9/0x110 mm/kasan/report.c:602
> >  folio_lock_anon_vma_read+0xc4e/0xd40 mm/rmap.c:559
> >  rmap_walk_anon_lock mm/rmap.c:2579 [inline]
> >  rmap_walk_anon+0x485/0x710 mm/rmap.c:2627
> >  rmap_walk mm/rmap.c:2724 [inline]
> >  rmap_walk mm/rmap.c:2719 [inline]
> >  folio_referenced+0x2a8/0x5c0 mm/rmap.c:1015
> >  folio_check_references mm/vmscan.c:896 [inline]
> >  shrink_folio_list+0x1dee/0x40c0 mm/vmscan.c:1234
> >  evict_folios+0x774/0x1ab0 mm/vmscan.c:4660
> >  try_to_shrink_lruvec+0x5a2/0x9a0 mm/vmscan.c:4821
> >  lru_gen_shrink_lruvec mm/vmscan.c:4970 [inline]
> >  shrink_lruvec+0x313/0x2ba0 mm/vmscan.c:5715
> >  shrink_node_memcgs mm/vmscan.c:5951 [inline]
> >  shrink_node mm/vmscan.c:5992 [inline]
> >  shrink_node+0x105c/0x3f20 mm/vmscan.c:5970
> >  shrink_zones mm/vmscan.c:6237 [inline]
> >  do_try_to_free_pages+0x35f/0x1a30 mm/vmscan.c:6299
> >  try_to_free_mem_cgroup_pages+0x31a/0x7a0 mm/vmscan.c:6631
> >  try_charge_memcg+0x356/0xaf0 mm/memcontrol.c:2255
> >  try_charge mm/memcontrol-v1.h:19 [inline]
> >  charge_memcg+0x8a/0x310 mm/memcontrol.c:4487
> >  __mem_cgroup_charge+0x2b/0x1e0 mm/memcontrol.c:4504
> >  mem_cgroup_charge include/linux/memcontrol.h:644 [inline]
> >  shmem_alloc_and_add_folio+0x50a/0xc10 mm/shmem.c:1912
> >  shmem_get_folio_gfp+0x689/0x1530 mm/shmem.c:2522
> >  shmem_get_folio mm/shmem.c:2628 [inline]
> >  shmem_write_begin+0x161/0x300 mm/shmem.c:3278
> >  generic_perform_write+0x2ba/0x920 mm/filemap.c:4189
> >  shmem_file_write_iter+0x10e/0x140 mm/shmem.c:3454
> >  __kernel_write_iter+0x318/0xa90 fs/read_write.c:612
> >  dump_emit_page fs/coredump.c:884 [inline]
> >  dump_user_range+0x389/0x8c0 fs/coredump.c:945
> >  elf_core_dump+0x2787/0x3880 fs/binfmt_elf.c:2129
> >  do_coredump+0x304f/0x45d0 fs/coredump.c:758
> >  get_signal+0x23f3/0x2610 kernel/signal.c:3021
> >  arch_do_signal_or_restart+0x90/0x7e0 arch/x86/kernel/signal.c:337
> >  exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
> >  exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
> >  irqentry_exit_to_user_mode+0x13f/0x280 kernel/entry/common.c:231
> >  asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
> > RIP: 0033:0x4021000
> > Code: Unable to access opcode bytes at 0x4020fd6.
> > RSP: 002b:000000000000000d EFLAGS: 00010206
> > RAX: 0000000000000000 RBX: 00007fc4c91a5fa0 RCX: 00007fc4c8f8cde9
> > RDX: ffffffffffffffff RSI: 0000000000000005 RDI: 0000000000008001
> > RBP: 00007fc4c900e2a0 R08: 0000000000000006 R09: 0000000000000000
> > R10: ffffffffff600000 R11: 0000000000000246 R12: 0000000000000000
> > R13: 0000000000000000 R14: 00007fc4c91a5fa0 R15: 00007ffdab469bf8
> >  </TASK>
> >
> > Allocated by task 4636:
> >  kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
> >  kasan_save_track+0x14/0x30 mm/kasan/common.c:68
> >  unpoison_slab_object mm/kasan/common.c:319 [inline]
> >  __kasan_slab_alloc+0x89/0x90 mm/kasan/common.c:345
> >  kasan_slab_alloc include/linux/kasan.h:250 [inline]
> >  slab_post_alloc_hook mm/slub.c:4115 [inline]
> >  slab_alloc_node mm/slub.c:4164 [inline]
> >  kmem_cache_alloc_noprof+0x1c8/0x3b0 mm/slub.c:4171
> >  anon_vma_alloc mm/rmap.c:94 [inline]
> >  anon_vma_fork+0xe6/0x620 mm/rmap.c:360
> >  dup_mmap kernel/fork.c:711 [inline]
> >  dup_mm kernel/fork.c:1700 [inline]
> >  copy_mm+0x1b7b/0x2730 kernel/fork.c:1752
> >  copy_process+0x3e6d/0x6f20 kernel/fork.c:2403
> >  kernel_clone+0xfd/0x960 kernel/fork.c:2815
> >  __do_sys_clone+0xba/0x100 kernel/fork.c:2958
> >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > Freed by task 4644:
> >  kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
> >  kasan_save_track+0x14/0x30 mm/kasan/common.c:68
> >  kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:576
> >  poison_slab_object mm/kasan/common.c:247 [inline]
> >  __kasan_slab_free+0x51/0x70 mm/kasan/common.c:264
> >  kasan_slab_free include/linux/kasan.h:233 [inline]
> >  slab_free_hook mm/slub.c:2353 [inline]
> >  slab_free_after_rcu_debug+0x115/0x340 mm/slub.c:4659
> >  rcu_do_batch kernel/rcu/tree.c:2546 [inline]
> >  rcu_core+0x79d/0x14d0 kernel/rcu/tree.c:2802
> >  handle_softirqs+0x213/0x8f0 kernel/softirq.c:561
> >  __do_softirq kernel/softirq.c:595 [inline]
> >  invoke_softirq kernel/softirq.c:435 [inline]
> >  __irq_exit_rcu+0x109/0x170 kernel/softirq.c:662
> >  irq_exit_rcu+0x9/0x30 kernel/softirq.c:678
> >  instr_sysvec_call_function_single arch/x86/kernel/smp.c:266 [inline]
> >  sysvec_call_function_single+0xa4/0xc0 arch/x86/kernel/smp.c:266
> >  asm_sysvec_call_function_single+0x1a/0x20 arch/x86/include/asm/idtentry.h:709
> >
> > Last potentially related work creation:
> >  kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
> >  kasan_record_aux_stack+0xb8/0xd0 mm/kasan/generic.c:548
> >  slab_free_hook mm/slub.c:2314 [inline]
> >  slab_free mm/slub.c:4609 [inline]
> >  kmem_cache_free+0x166/0x4d0 mm/slub.c:4711
> >  anon_vma_free mm/rmap.c:137 [inline]
> >  __put_anon_vma+0x114/0x3a0 mm/rmap.c:2568
> >  put_anon_vma include/linux/rmap.h:116 [inline]
> >  unlink_anon_vmas+0x58a/0x820 mm/rmap.c:444
> >  free_pgtables+0x33c/0x950 mm/memory.c:408
> >  exit_mmap+0x406/0xba0 mm/mmap.c:1295
> >  __mmput+0x12a/0x410 kernel/fork.c:1356
> >  mmput+0x62/0x70 kernel/fork.c:1378
> >  exec_mmap fs/exec.c:1011 [inline]
> >  begin_new_exec+0x152b/0x3800 fs/exec.c:1267
> >  load_elf_binary+0x85c/0x4ff0 fs/binfmt_elf.c:1002
> >  search_binary_handler fs/exec.c:1775 [inline]
> >  exec_binprm fs/exec.c:1807 [inline]
> >  bprm_execve fs/exec.c:1859 [inline]
> >  bprm_execve+0x8dd/0x16d0 fs/exec.c:1835
> >  do_execveat_common.isra.0+0x4a2/0x610 fs/exec.c:1966
> >  do_execve fs/exec.c:2040 [inline]
> >  __do_sys_execve fs/exec.c:2116 [inline]
> >  __se_sys_execve fs/exec.c:2111 [inline]
> >  __x64_sys_execve+0x8c/0xb0 fs/exec.c:2111
> >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > The buggy address belongs to the object at ffff888012dd7ee0
> >  which belongs to the cache anon_vma of size 208
> > The buggy address is located 0 bytes inside of
> >  freed 208-byte region [ffff888012dd7ee0, ffff888012dd7fb0)
> >
> > The buggy address belongs to the physical page:
> > page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888012dd7440 pfn:0x12dd7
> > memcg:ffff88802647a401
> > flags: 0xfff00000000200(workingset|node=0|zone=1|lastcpupid=0x7ff)
> > page_type: f5(slab)
> > raw: 00fff00000000200 ffff88801c282140 ffff88801b0937c8 ffffea0000c9a210
> > raw: ffff888012dd7440 00000000000f000e 00000000f5000000 ffff88802647a401
> > 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 5503, tgid 5503 (dhcpcd), ts 67849640029, free_ts 55595562609
> >  set_page_owner include/linux/page_owner.h:32 [inline]
> >  post_alloc_hook+0x181/0x1b0 mm/page_alloc.c:1551
> >  prep_new_page mm/page_alloc.c:1559 [inline]
> >  get_page_from_freelist+0xfce/0x2f80 mm/page_alloc.c:3477
> >  __alloc_frozen_pages_noprof+0x221/0x2470 mm/page_alloc.c:4739
> >  alloc_pages_mpol+0x1fc/0x540 mm/mempolicy.c:2270
> >  alloc_slab_page mm/slub.c:2423 [inline]
> >  allocate_slab mm/slub.c:2587 [inline]
> >  new_slab+0x23d/0x330 mm/slub.c:2640
> >  ___slab_alloc+0xbfa/0x1600 mm/slub.c:3826
> >  __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3916
> >  __slab_alloc_node mm/slub.c:3991 [inline]
> >  slab_alloc_node mm/slub.c:4152 [inline]
> >  kmem_cache_alloc_noprof+0xeb/0x3b0 mm/slub.c:4171
> >  anon_vma_alloc mm/rmap.c:94 [inline]
> >  anon_vma_fork+0xe6/0x620 mm/rmap.c:360
> >  dup_mmap kernel/fork.c:711 [inline]
> >  dup_mm kernel/fork.c:1700 [inline]
> >  copy_mm+0x1b7b/0x2730 kernel/fork.c:1752
> >  copy_process+0x3e6d/0x6f20 kernel/fork.c:2403
> >  kernel_clone+0xfd/0x960 kernel/fork.c:2815
> >  __do_sys_clone+0xba/0x100 kernel/fork.c:2958
> >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > page last free pid 5502 tgid 5502 stack trace:
> >  reset_page_owner include/linux/page_owner.h:25 [inline]
> >  free_pages_prepare mm/page_alloc.c:1127 [inline]
> >  free_frozen_pages+0x6db/0xfb0 mm/page_alloc.c:2660
> >  __put_partials+0x14c/0x170 mm/slub.c:3153
> >  qlink_free mm/kasan/quarantine.c:163 [inline]
> >  qlist_free_all+0x4e/0x120 mm/kasan/quarantine.c:179
> >  kasan_quarantine_reduce+0x195/0x1e0 mm/kasan/quarantine.c:286
> >  __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:329
> >  kasan_slab_alloc include/linux/kasan.h:250 [inline]
> >  slab_post_alloc_hook mm/slub.c:4115 [inline]
> >  slab_alloc_node mm/slub.c:4164 [inline]
> >  kmem_cache_alloc_node_noprof+0x1ca/0x3b0 mm/slub.c:4216
> >  __alloc_skb+0x2b3/0x380 net/core/skbuff.c:668
> >  alloc_skb include/linux/skbuff.h:1331 [inline]
> >  netlink_alloc_large_skb+0x69/0x130 net/netlink/af_netlink.c:1196
> >  netlink_sendmsg+0x689/0xd70 net/netlink/af_netlink.c:1867
> >  sock_sendmsg_nosec net/socket.c:713 [inline]
> >  __sock_sendmsg net/socket.c:728 [inline]
> >  ____sys_sendmsg+0x9ae/0xb40 net/socket.c:2568
> >  ___sys_sendmsg+0x135/0x1e0 net/socket.c:2622
> >  __sys_sendmsg+0x16e/0x220 net/socket.c:2654
> >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > Memory state around the buggy address:
> >  ffff888012dd7d80: 00 00 fc fc fc fc fc fc fc fc fa fb fb fb fb fb
> >  ffff888012dd7e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > >ffff888012dd7e80: fb fb fb fb fc fc fc fc fc fc fc fc fa fb fb fb
> >                                                        ^
> >  ffff888012dd7f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >  ffff888012dd7f80: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
> > ==================================================================
> >
> >
> > ---
> > 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@googlegroups.com.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> >
> > If the report is already addressed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
> >
> > 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
> >