Re: KASAN: use-after-free Read in get_mem_cgroup_from_mm

[zhong jiang]

Hi, guys

I also hit the following issue. but it fails to reproduce the issue by the log.

it seems to the case that we access the mm->owner and deference it will result in the UAF.
But it should not be possible that we specify the incomplete process to be the mm->owner.

Any thoughts?

Thanks,
zhong jiang

On 2018/12/4 23:43, syzbot wrote:
> syzbot has found a reproducer for the following crash on:
>
> HEAD commit:    0072a0c14d5b Merge tag 'media/v4.20-4' of git://git.kernel..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11c885a3400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=b9cc5a440391cbfd
> dashboard link: https://syzkaller.appspot.com/bug?extid=cbb52e396df3e565ab02
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12835e25400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=172fa5a3400000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+cbb52e396df3e565ab02@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> cgroup: fork rejected by pids controller in /syz2
> ==================================================================
> BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:182 [inline]
> BUG: KASAN: use-after-free in task_css include/linux/cgroup.h:477 [inline]
> BUG: KASAN: use-after-free in mem_cgroup_from_task mm/memcontrol.c:815 [inline]
> BUG: KASAN: use-after-free in get_mem_cgroup_from_mm.part.62+0x6d7/0x880 mm/memcontrol.c:844
> Read of size 8 at addr ffff8881b72af310 by task syz-executor198/9332
>
> CPU: 0 PID: 9332 Comm: syz-executor198 Not tainted 4.20.0-rc5+ #142
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x244/0x39d lib/dump_stack.c:113
>  print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>  __read_once_size include/linux/compiler.h:182 [inline]
>  task_css include/linux/cgroup.h:477 [inline]
>  mem_cgroup_from_task mm/memcontrol.c:815 [inline]
>  get_mem_cgroup_from_mm.part.62+0x6d7/0x880 mm/memcontrol.c:844
>  get_mem_cgroup_from_mm mm/memcontrol.c:834 [inline]
>  mem_cgroup_try_charge+0x608/0xe20 mm/memcontrol.c:5888
>  mcopy_atomic_pte mm/userfaultfd.c:71 [inline]
>  mfill_atomic_pte mm/userfaultfd.c:418 [inline]
>  __mcopy_atomic mm/userfaultfd.c:559 [inline]
>  mcopy_atomic+0xb08/0x2c70 mm/userfaultfd.c:609
>  userfaultfd_copy fs/userfaultfd.c:1705 [inline]
>  userfaultfd_ioctl+0x29fb/0x5610 fs/userfaultfd.c:1851
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  file_ioctl fs/ioctl.c:509 [inline]
>  do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
>  ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
>  __do_sys_ioctl fs/ioctl.c:720 [inline]
>  __se_sys_ioctl fs/ioctl.c:718 [inline]
>  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x44c7e9
> Code: 5d c5 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 2b c5 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f906b69fdb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00000000006e4a08 RCX: 000000000044c7e9
> RDX: 0000000020000100 RSI: 00000000c028aa03 RDI: 0000000000000004
> RBP: 00000000006e4a00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006e4a0c
> R13: 00007ffdfd47813f R14: 00007f906b6a09c0 R15: 000000000000002d
>
> Allocated by task 9325:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
>  kmem_cache_alloc_node+0x144/0x730 mm/slab.c:3644
>  alloc_task_struct_node kernel/fork.c:158 [inline]
>  dup_task_struct kernel/fork.c:843 [inline]
>  copy_process+0x2026/0x87a0 kernel/fork.c:1751
>  _do_fork+0x1cb/0x11d0 kernel/fork.c:2216
>  __do_sys_clone kernel/fork.c:2323 [inline]
>  __se_sys_clone kernel/fork.c:2317 [inline]
>  __x64_sys_clone+0xbf/0x150 kernel/fork.c:2317
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 9325:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>  __cache_free mm/slab.c:3498 [inline]
>  kmem_cache_free+0x83/0x290 mm/slab.c:3760
>  free_task_struct kernel/fork.c:163 [inline]
>  free_task+0x16e/0x1f0 kernel/fork.c:457
>  copy_process+0x1dcc/0x87a0 kernel/fork.c:2148
>  _do_fork+0x1cb/0x11d0 kernel/fork.c:2216
>  __do_sys_clone kernel/fork.c:2323 [inline]
>  __se_sys_clone kernel/fork.c:2317 [inline]
>  __x64_sys_clone+0xbf/0x150 kernel/fork.c:2317
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff8881b72ae240
>  which belongs to the cache task_struct(81:syz2) of size 6080
> The buggy address is located 4304 bytes inside of
>  6080-byte region [ffff8881b72ae240, ffff8881b72afa00)
> The buggy address belongs to the page:
> page:ffffea0006dcab80 count:1 mapcount:0 mapping:ffff8881d2dce0c0 index:0x0 compound_mapcount: 0
> flags: 0x2fffc0000010200(slab|head)
> raw: 02fffc0000010200 ffffea00074a1f88 ffffea0006ebbb88 ffff8881d2dce0c0
> raw: 0000000000000000 ffff8881b72ae240 0000000100000001 ffff8881d87fe580
> page dumped because: kasan: bad access detected
> page->mem_cgroup:ffff8881d87fe580
>
> Memory state around the buggy address:
>  ffff8881b72af200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8881b72af280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff8881b72af300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                          ^
>  ffff8881b72af380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8881b72af400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
>
> .
>