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Date:   Mon, 21 Jun 2021 15:37:34 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     syzbot <syzbot+7b2b13f4943374609532@syzkaller.appspotmail.com>
Cc:     akpm@linux-foundation.org, andrii@kernel.org, ast@kernel.org,
        axboe@kernel.dk, bpf@vger.kernel.org, christian@brauner.io,
        daniel@iogearbox.net, dvyukov@google.com, jiangshanlai@gmail.com,
        joel@joelfernandes.org, john.fastabend@gmail.com,
        josh@joshtriplett.org, kafai@fb.com, kpsingh@kernel.org,
        linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com,
        netdev@vger.kernel.org, peterz@infradead.org, rcu@vger.kernel.org,
        rostedt@goodmis.org, shakeelb@google.com, songliubraving@fb.com,
        syzkaller-bugs@googlegroups.com, yanfei.xu@windriver.com,
        yhs@fb.com
Subject: Re: [syzbot] KASAN: use-after-free Read in
 check_all_holdout_tasks_trace
Message-ID: <20210621223734.GV4397@paulmck-ThinkPad-P17-Gen-1>
Reply-To: paulmck@kernel.org
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 <00000000000022183205c5106739@google.com>
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On Fri, Jun 18, 2021 at 01:45:23PM -0700, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    0c38740c selftests/bpf: Fix ringbuf test fetching map FD
> git tree:       bpf-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=128a7e34300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a6380da8984033f1
> dashboard link: https://syzkaller.appspot.com/bug?extid=7b2b13f4943374609532
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1264c2d7d00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+7b2b13f4943374609532@syzkaller.appspotmail.com

This looks like a bug that Xu Yanfei located a few weeks back.

Do these commits from -rcu help?

6a04a59eacbd ("rcu-tasks: Don't delete holdouts within trc_inspect_reader()"
dd5da0a9140e ("rcu-tasks: Don't delete holdouts within trc_wait_for_one_reader()")

On any interaction with the HEAD commit above I must defer to Andrii.

							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 ffff8880294cbc9c by task rcu_tasks_trace/12
> 
> CPU: 0 PID: 12 Comm: rcu_tasks_trace Not tainted 5.13.0-rc3-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 8499:
>  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:2913 [inline]
>  kmem_cache_alloc_node+0x269/0x3e0 mm/slub.c:2949
>  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:1582 [inline]
>  slab_free_freelist_hook+0xdf/0x240 mm/slub.c:1607
>  slab_free mm/slub.c:3167 [inline]
>  kmem_cache_free+0x8a/0x740 mm/slub.c:3183
>  __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
>  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
> 
> The buggy address belongs to the object at ffff8880294cb880
>  which belongs to the cache task_struct of size 6976
> The buggy address is located 1052 bytes inside of
>  6976-byte region [ffff8880294cb880, ffff8880294cd3c0)
> The buggy address belongs to the page:
> page:ffffea0000a53200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x294c8
> head:ffffea0000a53200 order:3 compound_mapcount:0 compound_pincount:0
> flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000010200 ffffea00008d6400 0000000200000002 ffff888140005140
> raw: 0000000000000000 0000000000040004 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 2, ts 15187628853, free_ts 0
>  prep_new_page mm/page_alloc.c:2358 [inline]
>  get_page_from_freelist+0x1034/0x2bf0 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:1645 [inline]
>  allocate_slab+0x32e/0x4c0 mm/slub.c:1785
>  new_slab mm/slub.c:1848 [inline]
>  new_slab_objects mm/slub.c:2594 [inline]
>  ___slab_alloc+0x4a1/0x810 mm/slub.c:2757
>  __slab_alloc.constprop.0+0xa7/0xf0 mm/slub.c:2797
>  slab_alloc_node mm/slub.c:2879 [inline]
>  kmem_cache_alloc_node+0x12f/0x3e0 mm/slub.c:2949
>  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
>  create_kthread kernel/kthread.c:336 [inline]
>  kthreadd+0x52a/0x790 kernel/kthread.c:679
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> page_owner free stack trace missing
> 
> Memory state around the buggy address:
>  ffff8880294cbb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880294cbc00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff8880294cbc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                             ^
>  ffff8880294cbd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880294cbd80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>