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Date:   Wed, 2 Sep 2020 09:05:35 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     syzbot <syzbot+5334f62e4d22804e646a@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, andriin@...com, ast@...nel.org,
        bjorn.topel@...el.com, bpf@...r.kernel.org, davem@...emloft.net,
        hawk@...nel.org, john.fastabend@...il.com,
        jonathan.lemon@...il.com, kafai@...com, kpsingh@...omium.org,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        magnus.karlsson@...el.com, mingo@...nel.org,
        netdev@...r.kernel.org, paulmck@...nel.org, peterz@...radead.org,
        songliubraving@...com, syzkaller-bugs@...glegroups.com,
        tglx@...utronix.de, yhs@...com
Subject: Re: KASAN: use-after-free Write in xp_put_pool

On 9/2/20 8:57 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:

Magnus/Bjorn, ptal, thanks!

> HEAD commit:    dc1a9bf2 octeontx2-pf: Add UDP segmentation offload support
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=16ff67de900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=b6856d16f78d8fa9
> dashboard link: https://syzkaller.appspot.com/bug?extid=5334f62e4d22804e646a
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12e9f279900000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=125f3e1e900000
> 
> The issue was bisected to:
> 
> commit a1132430c2c55af62d13e9fca752d46f14d548b3
> Author: Magnus Karlsson <magnus.karlsson@...el.com>
> Date:   Fri Aug 28 08:26:26 2020 +0000
> 
>      xsk: Add shared umem support between devices
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10a373de900000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=12a373de900000
> console output: https://syzkaller.appspot.com/x/log.txt?x=14a373de900000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+5334f62e4d22804e646a@...kaller.appspotmail.com
> Fixes: a1132430c2c5 ("xsk: Add shared umem support between devices")
> 
> ==================================================================
> BUG: KASAN: use-after-free in instrument_atomic_write include/linux/instrumented.h:71 [inline]
> BUG: KASAN: use-after-free in atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline]
> BUG: KASAN: use-after-free in refcount_sub_and_test include/linux/refcount.h:266 [inline]
> BUG: KASAN: use-after-free in refcount_dec_and_test include/linux/refcount.h:294 [inline]
> BUG: KASAN: use-after-free in xp_put_pool+0x2c/0x1e0 net/xdp/xsk_buff_pool.c:262
> Write of size 4 at addr ffff8880a6a4d860 by task ksoftirqd/0/9
> 
> CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 5.9.0-rc1-syzkaller #0
> 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+0x18f/0x20d lib/dump_stack.c:118
>   print_address_description.constprop.0.cold+0xae/0x497 mm/kasan/report.c:383
>   __kasan_report mm/kasan/report.c:513 [inline]
>   kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
>   check_memory_region_inline mm/kasan/generic.c:186 [inline]
>   check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
>   instrument_atomic_write include/linux/instrumented.h:71 [inline]
>   atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline]
>   refcount_sub_and_test include/linux/refcount.h:266 [inline]
>   refcount_dec_and_test include/linux/refcount.h:294 [inline]
>   xp_put_pool+0x2c/0x1e0 net/xdp/xsk_buff_pool.c:262
>   xsk_destruct+0x7d/0xa0 net/xdp/xsk.c:1138
>   __sk_destruct+0x4b/0x860 net/core/sock.c:1764
>   rcu_do_batch kernel/rcu/tree.c:2428 [inline]
>   rcu_core+0x5c7/0x1190 kernel/rcu/tree.c:2656
>   __do_softirq+0x2de/0xa24 kernel/softirq.c:298
>   run_ksoftirqd kernel/softirq.c:652 [inline]
>   run_ksoftirqd+0x89/0x100 kernel/softirq.c:644
>   smpboot_thread_fn+0x655/0x9e0 kernel/smpboot.c:165
>   kthread+0x3b5/0x4a0 kernel/kthread.c:292
>   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> 
> Allocated by task 6854:
>   kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>   kasan_set_track mm/kasan/common.c:56 [inline]
>   __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:461
>   kmalloc_node include/linux/slab.h:577 [inline]
>   kvmalloc_node+0x61/0xf0 mm/util.c:574
>   kvmalloc include/linux/mm.h:750 [inline]
>   kvzalloc include/linux/mm.h:758 [inline]
>   xp_create_and_assign_umem+0x58/0x8d0 net/xdp/xsk_buff_pool.c:54
>   xsk_bind+0x9a0/0xed0 net/xdp/xsk.c:709
>   __sys_bind+0x1e9/0x250 net/socket.c:1656
>   __do_sys_bind net/socket.c:1667 [inline]
>   __se_sys_bind net/socket.c:1665 [inline]
>   __x64_sys_bind+0x6f/0xb0 net/socket.c:1665
>   do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Freed by task 6854:
>   kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>   kasan_set_track+0x1c/0x30 mm/kasan/common.c:56
>   kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:355
>   __kasan_slab_free+0xd8/0x120 mm/kasan/common.c:422
>   __cache_free mm/slab.c:3418 [inline]
>   kfree+0x103/0x2c0 mm/slab.c:3756
>   kvfree+0x42/0x50 mm/util.c:603
>   xp_destroy net/xdp/xsk_buff_pool.c:44 [inline]
>   xp_destroy+0x45/0x60 net/xdp/xsk_buff_pool.c:38
>   xsk_bind+0xbdd/0xed0 net/xdp/xsk.c:719
>   __sys_bind+0x1e9/0x250 net/socket.c:1656
>   __do_sys_bind net/socket.c:1667 [inline]
>   __se_sys_bind net/socket.c:1665 [inline]
>   __x64_sys_bind+0x6f/0xb0 net/socket.c:1665
>   do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> The buggy address belongs to the object at ffff8880a6a4d800
>   which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 96 bytes inside of
>   1024-byte region [ffff8880a6a4d800, ffff8880a6a4dc00)
> The buggy address belongs to the page:
> page:00000000dd5fc18f refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xa6a4d
> flags: 0xfffe0000000200(slab)
> raw: 00fffe0000000200 ffffea00029cce48 ffffea00025f2148 ffff8880aa040700
> raw: 0000000000000000 ffff8880a6a4d000 0000000100000002 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>   ffff8880a6a4d700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>   ffff8880a6a4d780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>> ffff8880a6a4d800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                         ^
>   ffff8880a6a4d880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff8880a6a4d900: 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@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
> 

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