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Subject: Re: KASAN: use-after-free Read in bpf_cgroup_storage_release
To:     syzbot <syzbot+25554ab865a12b51c66f@syzkaller.appspotmail.com>,
        ast@kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        guro@fb.com
References: <000000000000f3b1570572779079@google.com>
From:   Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <1b3dde38-549e-43ed-d3f6-18b451444d2f@iogearbox.net>
Date:   Thu, 2 Aug 2018 21:23:00 +0200
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[ +Roman ]

On 08/02/2018 07:59 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    fc2a3b5dd618 Merge branch 'bpf-cgroup-local-storage'
> git tree:       bpf-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=17a6a1c8400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3bfcc1651962483
> dashboard link: https://syzkaller.appspot.com/bug?extid=25554ab865a12b51c66f
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=12c4b9b4400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13e9d6f0400000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+25554ab865a12b51c66f@syzkaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: use-after-free in debug_spin_lock_before kernel/locking/spinlock_debug.c:83 [inline]
> BUG: KASAN: use-after-free in do_raw_spin_lock+0x1c0/0x200 kernel/locking/spinlock_debug.c:112
> Read of size 4 at addr ffff8801c4723644 by task syz-executor865/9746
> 
> CPU: 0 PID: 9746 Comm: syz-executor865 Not tainted 4.18.0-rc5+ #68
> 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+0x1c9/0x2b4 lib/dump_stack.c:113
>  print_address_description+0x6c/0x20b mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
>  __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
>  debug_spin_lock_before kernel/locking/spinlock_debug.c:83 [inline]
>  do_raw_spin_lock+0x1c0/0x200 kernel/locking/spinlock_debug.c:112
>  __raw_spin_lock_bh include/linux/spinlock_api_smp.h:136 [inline]
>  _raw_spin_lock_bh+0x39/0x40 kernel/locking/spinlock.c:168
>  spin_lock_bh include/linux/spinlock.h:315 [inline]
>  bpf_cgroup_storage_release+0x2c/0x110 kernel/bpf/local_storage.c:276
>  free_used_maps+0x81/0x200 kernel/bpf/syscall.c:961
>  bpf_prog_load+0x17ba/0x1c90 kernel/bpf/syscall.c:1414
>  __do_sys_bpf kernel/bpf/syscall.c:2338 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:2300 [inline]
>  __x64_sys_bpf+0x36c/0x510 kernel/bpf/syscall.c:2300
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x4490d9
> Code: e8 8c bb 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 4b 00 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f6096d1ace8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 00000000006e5a08 RCX: 00000000004490d9
> RDX: 0000000000000048 RSI: 000000002001a840 RDI: 0000000000000005
> RBP: 00000000006e5a00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006e5a0c
> R13: 00007fffd579e24f R14: 00007f6096d1b9c0 R15: 0000000000000019
> 
> Allocated by task 9746:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
>  kmem_cache_alloc_node_trace+0x150/0x770 mm/slab.c:3663
>  kmalloc_node include/linux/slab.h:551 [inline]
>  cgroup_storage_map_alloc+0x26d/0x400 kernel/bpf/local_storage.c:209
>  find_and_alloc_map kernel/bpf/syscall.c:129 [inline]
>  map_create+0x37f/0xe20 kernel/bpf/syscall.c:481
>  __do_sys_bpf kernel/bpf/syscall.c:2323 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:2300 [inline]
>  __x64_sys_bpf+0x303/0x510 kernel/bpf/syscall.c:2300
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Freed by task 19:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>  __cache_free mm/slab.c:3498 [inline]
>  kfree+0xd9/0x260 mm/slab.c:3813
>  cgroup_storage_map_free+0x16e/0x210 kernel/bpf/local_storage.c:234
>  bpf_map_free_deferred+0xba/0xf0 kernel/bpf/syscall.c:290
>  process_one_work+0xc73/0x1ba0 kernel/workqueue.c:2153
>  worker_thread+0x189/0x13c0 kernel/workqueue.c:2296
>  kthread+0x345/0x410 kernel/kthread.c:246
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
> 
> The buggy address belongs to the object at ffff8801c4723540
>  which belongs to the cache kmalloc-512 of size 512
> The buggy address is located 260 bytes inside of
>  512-byte region [ffff8801c4723540, ffff8801c4723740)
> The buggy address belongs to the page:
> page:ffffea000711c8c0 count:1 mapcount:0 mapping:ffff8801dac00940 index:0xffff8801c4723a40
> flags: 0x2fffc0000000100(slab)
> raw: 02fffc0000000100 ffffea0007299088 ffffea00072247c8 ffff8801dac00940
> raw: ffff8801c4723a40 ffff8801c4723040 0000000100000004 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8801c4723500: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>  ffff8801c4723580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff8801c4723600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                            ^
>  ffff8801c4723680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801c4723700: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ==================================================================
> 
> 
> ---
> This bug 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@googlegroups.com.
> 
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