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Date:   Thu, 10 Mar 2022 13:06:26 -0800
From:   Martin KaFai Lau <kafai@fb.com>
To:     toke@redhat.com
Cc:     andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
        daniel@iogearbox.net, davem@davemloft.net, hawk@kernel.org,
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        syzbot <syzbot+0e91362d99386dc5de99@syzkaller.appspotmail.com>
Subject: Re: [syzbot] BUG: missing reserved tailroom
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On Thu, Mar 10, 2022 at 10:37:20AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    de55c9a1967c Merge branch 'Add support for transmitting pa..
> git tree:       bpf-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=14ce88ad700000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2fa13781bcea50fc
> dashboard link: https://syzkaller.appspot.com/bug?extid=0e91362d99386dc5de99
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11f36345700000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14c8ca65700000
> 
> The issue was bisected to:
> 
> commit b530e9e1063ed2b817eae7eec6ed2daa8be11608
> Author: Toke H?iland-J?rgensen <toke@redhat.com>
> Date:   Wed Mar 9 10:53:42 2022 +0000
> 
>     bpf: Add "live packet" mode for XDP in BPF_PROG_RUN
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17696e55700000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=14e96e55700000
> console output: https://syzkaller.appspot.com/x/log.txt?x=10e96e55700000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+0e91362d99386dc5de99@syzkaller.appspotmail.com
> Fixes: b530e9e1063e ("bpf: Add "live packet" mode for XDP in BPF_PROG_RUN")
> 
> ------------[ cut here ]------------
> XDP_WARN: xdp_update_frame_from_buff(line:274): Driver BUG: missing reserved tailroom
> WARNING: CPU: 0 PID: 3590 at net/core/xdp.c:599 xdp_warn+0x28/0x30 net/core/xdp.c:599
Toke, please take a look.


> Modules linked in:
> CPU: 0 PID: 3590 Comm: syz-executor167 Not tainted 5.17.0-rc6-syzkaller-01958-gde55c9a1967c #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:xdp_warn+0x28/0x30 net/core/xdp.c:599
> Code: 40 00 41 55 49 89 fd 41 54 41 89 d4 55 48 89 f5 e8 2d 08 3a fa 4c 89 e9 44 89 e2 48 89 ee 48 c7 c7 80 ea b0 8a e8 ef c7 cd 01 <0f> 0b 5d 41 5c 41 5d c3 55 53 48 89 fb e8 06 08 3a fa 48 8d 7b ec
> RSP: 0018:ffffc9000370f6f8 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: ffff888018d8a198 RCX: 0000000000000000
> RDX: ffff88802272d700 RSI: ffffffff815fe2c8 RDI: fffff520006e1ed1
> RBP: ffffffff8ab54aa0 R08: 0000000000000000 R09: 0000000000000001
> R10: ffffffff815f895e R11: 0000000000000000 R12: 0000000000000112
> R13: ffffffff8ab54780 R14: ffff888018d8a000 R15: ffff888018d8ae98
> FS:  000055555694a300(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020001000 CR3: 000000007255a000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  xdp_update_frame_from_buff include/net/xdp.h:274 [inline]
>  xdp_update_frame_from_buff include/net/xdp.h:260 [inline]
>  xdp_test_run_init_page+0x3f1/0x500 net/bpf/test_run.c:143
>  page_pool_set_pp_info net/core/page_pool.c:268 [inline]
>  __page_pool_alloc_pages_slow+0x269/0x1050 net/core/page_pool.c:339
>  page_pool_alloc_pages+0xb6/0x100 net/core/page_pool.c:372
>  page_pool_dev_alloc_pages include/net/page_pool.h:197 [inline]
>  xdp_test_run_batch net/bpf/test_run.c:280 [inline]
>  bpf_test_run_xdp_live+0x53a/0x18c0 net/bpf/test_run.c:363
>  bpf_prog_test_run_xdp+0x8f6/0x1440 net/bpf/test_run.c:1317
>  bpf_prog_test_run kernel/bpf/syscall.c:3363 [inline]
>  __sys_bpf+0x1858/0x59a0 kernel/bpf/syscall.c:4665
>  __do_sys_bpf kernel/bpf/syscall.c:4751 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:4749 [inline]
>  __x64_sys_bpf+0x75/0xb0 kernel/bpf/syscall.c:4749
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7fc3679a71f9
> Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 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 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffdd3b6d268 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc3679a71f9
> RDX: 0000000000000048 RSI: 0000000020000000 RDI: 000000000000000a
> RBP: 00007fc36796b1e0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007fc36796b270
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>  </TASK>
> 
> 
> ---
> 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@googlegroups.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