On Mon, Mar 4, 2019 at 4:32 PM zhong jiang <zhongjiang@xxxxxxxxxx> wrote: > > On 2019/3/4 22:11, Dmitry Vyukov wrote: > > On Mon, Mar 4, 2019 at 3:00 PM zhong jiang <zhongjiang@xxxxxxxxxx> wrote: > >> On 2019/3/4 15:40, Dmitry Vyukov wrote: > >>> On Sun, Mar 3, 2019 at 5:19 PM zhong jiang <zhongjiang@xxxxxxxxxx> wrote: > >>>> 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? > >>> FWIW syzbot was able to reproduce this with this reproducer. > >>> This looks like a very subtle race (threaded reproducer that runs > >>> repeatedly in multiple processes), so most likely we are looking for > >>> something like few instructions inconsistency window. > >>> > >> I has a little doubtful about the instrustions inconsistency window. > >> > >> I guess that you mean some smb barriers should be taken into account.:-) > >> > >> Because IMO, It should not be the lock case to result in the issue. > > > > Since the crash was triggered on x86 _most likley_ this is not a > > missed barrier. What I meant is that one thread needs to executed some > > code, while another thread is stopped within few instructions. > > > > > It is weird and I can not find any relationship you had said with the issue.:-( > > Because It is the cause that mm->owner has been freed, whereas we still deference it. > > From the lastest freed task call trace, It fails to create process. > > Am I miss something or I misunderstand your meaning. Please correct me. Your analysis looks correct. I am just saying that the root cause of this use-after-free seems to be a race condition. > >>>> 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 > >>>>> ================================================================== > >>>>> > >>>>> > >>>>> . > >>>>> > >>>> -- > >>>> You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. > >>>> To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@xxxxxxxxxxxxxxxx. > >>>> To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/5C7BFE94.6070500%40huawei.com. > >>>> For more options, visit https://groups.google.com/d/optout. > >>> . > >>> > >> > > . > > > >
