On Sun, May 23, 2021 at 09:13:50PM -0700, Paul E. McKenney wrote: > On Sun, May 23, 2021 at 08:51:56AM +0200, Dmitry Vyukov wrote: > > On Fri, May 21, 2021 at 7:29 PM syzbot > > <syzbot+7b2b13f4943374609532@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > Hello, > > > > > > syzbot found the following issue on: > > > > > > HEAD commit: f18ba26d libbpf: Add selftests for TC-BPF management API > > > git tree: bpf-next > > > console output: https://syzkaller.appspot.com/x/log.txt?x=17f50d1ed00000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=8ff54addde0afb5d > > > dashboard link: https://syzkaller.appspot.com/bug?extid=7b2b13f4943374609532 > > > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > Reported-by: syzbot+7b2b13f4943374609532@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > This looks rcu-related. +rcu mailing list > > I think I see a possible cause for this, and will say more after some > testing and after becoming more awake Monday morning, Pacific time. No joy. From what I can see, within RCU Tasks Trace, the calls to get_task_struct() are properly protected (either by RCU or by an earlier get_task_struct()), and the calls to put_task_struct() are balanced by those to get_task_struct(). I could of course have missed something, but at this point I am suspecting an unbalanced put_task_struct() has been added elsewhere. As always, extra eyes on this code would be a good thing. If it were reproducible, I would of course suggest bisection. :-/ Thanx, Paul > > > ================================================================== > > > BUG: KASAN: use-after-free in check_all_holdout_tasks_trace+0x302/0x420 kernel/rcu/tasks.h:1084 > > > Read of size 1 at addr ffff88802767a05c by task rcu_tasks_trace/12 > > > > > > CPU: 0 PID: 12 Comm: rcu_tasks_trace Not tainted 5.12.0-syzkaller #0 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > > Call Trace: > > > __dump_stack lib/dump_stack.c:79 [inline] > > > dump_stack+0x141/0x1d7 lib/dump_stack.c:120 > > > print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:233 > > > __kasan_report mm/kasan/report.c:419 [inline] > > > kasan_report.cold+0x7c/0xd8 mm/kasan/report.c:436 > > > check_all_holdout_tasks_trace+0x302/0x420 kernel/rcu/tasks.h:1084 > > > rcu_tasks_wait_gp+0x594/0xa60 kernel/rcu/tasks.h:358 > > > rcu_tasks_kthread+0x31c/0x6a0 kernel/rcu/tasks.h:224 > > > kthread+0x3b1/0x4a0 kernel/kthread.c:313 > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 > > > > > > Allocated by task 8477: > > > kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 > > > kasan_set_track mm/kasan/common.c:46 [inline] > > > set_alloc_info mm/kasan/common.c:428 [inline] > > > __kasan_slab_alloc+0x84/0xa0 mm/kasan/common.c:461 > > > kasan_slab_alloc include/linux/kasan.h:236 [inline] > > > slab_post_alloc_hook mm/slab.h:524 [inline] > > > slab_alloc_node mm/slub.c:2912 [inline] > > > kmem_cache_alloc_node+0x269/0x3e0 mm/slub.c:2948 > > > alloc_task_struct_node kernel/fork.c:171 [inline] > > > dup_task_struct kernel/fork.c:865 [inline] > > > copy_process+0x5c8/0x7120 kernel/fork.c:1947 > > > kernel_clone+0xe7/0xab0 kernel/fork.c:2503 > > > __do_sys_clone+0xc8/0x110 kernel/fork.c:2620 > > > do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47 > > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > > > > > Freed by task 12: > > > kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 > > > kasan_set_track+0x1c/0x30 mm/kasan/common.c:46 > > > kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:357 > > > ____kasan_slab_free mm/kasan/common.c:360 [inline] > > > ____kasan_slab_free mm/kasan/common.c:325 [inline] > > > __kasan_slab_free+0xfb/0x130 mm/kasan/common.c:368 > > > kasan_slab_free include/linux/kasan.h:212 [inline] > > > slab_free_hook mm/slub.c:1581 [inline] > > > slab_free_freelist_hook+0xdf/0x240 mm/slub.c:1606 > > > slab_free mm/slub.c:3166 [inline] > > > kmem_cache_free+0x8a/0x740 mm/slub.c:3182 > > > __put_task_struct+0x26f/0x400 kernel/fork.c:747 > > > trc_wait_for_one_reader kernel/rcu/tasks.h:935 [inline] > > > check_all_holdout_tasks_trace+0x179/0x420 kernel/rcu/tasks.h:1081 > > > rcu_tasks_wait_gp+0x594/0xa60 kernel/rcu/tasks.h:358 > > > rcu_tasks_kthread+0x31c/0x6a0 kernel/rcu/tasks.h:224 > > > kthread+0x3b1/0x4a0 kernel/kthread.c:313 > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 > > > > > > Last potentially related work creation: > > > kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 > > > kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:345 > > > __call_rcu kernel/rcu/tree.c:3038 [inline] > > > call_rcu+0xb1/0x750 kernel/rcu/tree.c:3113 > > > put_task_struct_rcu_user+0x7f/0xb0 kernel/exit.c:180 > > > release_task+0xca1/0x1690 kernel/exit.c:226 > > > wait_task_zombie kernel/exit.c:1108 [inline] > > > wait_consider_task+0x2fb5/0x3b40 kernel/exit.c:1335 > > > do_wait_thread kernel/exit.c:1398 [inline] > > > do_wait+0x724/0xd40 kernel/exit.c:1515 > > > kernel_wait4+0x14c/0x260 kernel/exit.c:1678 > > > __do_sys_wait4+0x13f/0x150 kernel/exit.c:1706 > > > do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47 > > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > > > > > Second to last potentially related work creation: > > > kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 > > > kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:345 > > > __call_rcu kernel/rcu/tree.c:3038 [inline] > > > call_rcu+0xb1/0x750 kernel/rcu/tree.c:3113 > > > put_task_struct_rcu_user+0x7f/0xb0 kernel/exit.c:180 > > > context_switch kernel/sched/core.c:4342 [inline] > > > __schedule+0x91e/0x23e0 kernel/sched/core.c:5147 > > > preempt_schedule_common+0x45/0xc0 kernel/sched/core.c:5307 > > > preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:35 > > > try_to_wake_up+0xa12/0x14b0 kernel/sched/core.c:3489 > > > wake_up_process kernel/sched/core.c:3552 [inline] > > > wake_up_q+0x96/0x100 kernel/sched/core.c:597 > > > futex_wake+0x3e9/0x490 kernel/futex.c:1634 > > > do_futex+0x326/0x1780 kernel/futex.c:3738 > > > __do_sys_futex+0x2a2/0x470 kernel/futex.c:3796 > > > do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47 > > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > > > > > The buggy address belongs to the object at ffff888027679c40 > > > which belongs to the cache task_struct of size 6976 > > > The buggy address is located 1052 bytes inside of > > > 6976-byte region [ffff888027679c40, ffff88802767b780) > > > The buggy address belongs to the page: > > > page:ffffea00009d9e00 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88802767b880 pfn:0x27678 > > > head:ffffea00009d9e00 order:3 compound_mapcount:0 compound_pincount:0 > > > flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff) > > > raw: 00fff00000010200 ffffea000071e208 ffffea0000950808 ffff888140005140 > > > raw: ffff88802767b880 0000000000040003 00000001ffffffff 0000000000000000 > > > page dumped because: kasan: bad access detected > > > page_owner tracks the page as allocated > > > page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 243, ts 14372676818, free_ts 0 > > > prep_new_page mm/page_alloc.c:2358 [inline] > > > get_page_from_freelist+0x1033/0x2b60 mm/page_alloc.c:3994 > > > __alloc_pages+0x1b2/0x500 mm/page_alloc.c:5200 > > > alloc_pages+0x18c/0x2a0 mm/mempolicy.c:2272 > > > alloc_slab_page mm/slub.c:1644 [inline] > > > allocate_slab+0x2c5/0x4c0 mm/slub.c:1784 > > > new_slab mm/slub.c:1847 [inline] > > > new_slab_objects mm/slub.c:2593 [inline] > > > ___slab_alloc+0x44c/0x7a0 mm/slub.c:2756 > > > __slab_alloc.constprop.0+0xa7/0xf0 mm/slub.c:2796 > > > slab_alloc_node mm/slub.c:2878 [inline] > > > kmem_cache_alloc_node+0x12f/0x3e0 mm/slub.c:2948 > > > alloc_task_struct_node kernel/fork.c:171 [inline] > > > dup_task_struct kernel/fork.c:865 [inline] > > > copy_process+0x5c8/0x7120 kernel/fork.c:1947 > > > kernel_clone+0xe7/0xab0 kernel/fork.c:2503 > > > kernel_thread+0xb5/0xf0 kernel/fork.c:2555 > > > call_usermodehelper_exec_work kernel/umh.c:174 [inline] > > > call_usermodehelper_exec_work+0xcc/0x180 kernel/umh.c:160 > > > process_one_work+0x98d/0x1600 kernel/workqueue.c:2275 > > > worker_thread+0x64c/0x1120 kernel/workqueue.c:2421 > > > kthread+0x3b1/0x4a0 kernel/kthread.c:313 > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 > > > page_owner free stack trace missing > > > > > > Memory state around the buggy address: > > > ffff888027679f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > > ffff888027679f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > > >ffff88802767a000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > > ^ > > > ffff88802767a080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > > ffff88802767a100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > > ================================================================== > > > > > > > > > --- > > > 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@xxxxxxxxxxxxxxxx. > > > > > > syzbot will keep track of this issue. See: > > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > > > > > -- > > > 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/000000000000f034fc05c2da6617%40google.com.
