On 2019/3/5 5:51, Matthew Wilcox wrote: > On Mon, Mar 04, 2019 at 12:19:32AM +0800, zhong jiang wrote: >> 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. > OK, so we've got thread 9325 calling fork() and failing due to the PID > controller saying "no". 9325 calls free_task(), but somehow thread 9332 > has a reference to the struct task_struct. There are two possibilities > here: one is that 9332 really did manage to get a reference to the larval > child of 9325, and the other is that 9332 has a stale reference to some > memory which was reallocated to 9325's child. Good guess and analysis. IMO, 9332 can not handle the task_struct directly in the code flow. But It can get a reference of mm_struct. Maybe I miss something important. > Andrea, is there any way for a UFFD thread to get access to the child's > task_struct during the copy_process() call? If so, I think copy_process() > needs to call mm_update_next_owner(). Yep, Hope andrea have time to look at this. Thanks, zhong jiang > If there's no way for that to happen, then we have quite a bug-hunt ahead > of us looking for who is missing a call to mm_update_next_owner(). >> 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 >>> ================================================================== >>> >>> >>> . >>> >> > . >
