On 2019/3/5 14:26, Dmitry Vyukov wrote: > 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. > > > Yep, Indeed, I can not figure out how the race works. I will dig up further. 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 >>>>>>> ================================================================== >>>>>>> >>>>>>> >>>>>>> . >>>>>>> >>>>>> -- >>>>>> 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. >>>>> . >>>>> >>> . >>> >> > . >
