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Message-ID: <6b48673b-33a2-877d-dadd-b43a1364b330@intel.com>
Date: Wed, 15 Mar 2023 13:10:44 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: <ast@...nel.org>,
Toke Høiland-Jørgensen <toke@...hat.com>
CC: syzbot <syzbot+e1d1b65f7c32f2a86a9f@...kaller.appspotmail.com>,
<bpf@...r.kernel.org>, <daniel@...earbox.net>,
<davem@...emloft.net>, <edumazet@...gle.com>, <hawk@...nel.org>,
<john.fastabend@...il.com>, <kuba@...nel.org>,
<linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
<pabeni@...hat.com>, <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] [bpf?] [net?] BUG: unable to handle kernel NULL pointer
dereference in __build_skb_around
From: Syzbot <syzbot+e1d1b65f7c32f2a86a9f@...kaller.appspotmail.com>
Date: Wed, 15 Mar 2023 05:03:47 -0700
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 3c2611bac08a selftests/bpf: Fix trace_virtqueue_add_sgs te..
> git tree: bpf-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1026d472c80000
> kernel config: https://syzkaller.appspot.com/x/.config?x=cab35c936731a347
> dashboard link: https://syzkaller.appspot.com/bug?extid=e1d1b65f7c32f2a86a9f
> 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=15826bc6c80000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15cd12e2c80000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/36a32f4d222a/disk-3c2611ba.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/f5c0da04f143/vmlinux-3c2611ba.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/ae2ca9bce51a/bzImage-3c2611ba.xz
>
> The issue was bisected to:
>
> commit 9c94bbf9a87b264294f42e6cc0f76d87854733ec
> Author: Alexander Lobakin <aleksander.lobakin@...el.com>
> Date: Mon Mar 13 21:55:52 2023 +0000
>
> xdp: recycle Page Pool backed skbs built from XDP frames
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=11deec2ac80000
> final oops: https://syzkaller.appspot.com/x/report.txt?x=13deec2ac80000
> console output: https://syzkaller.appspot.com/x/log.txt?x=15deec2ac80000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+e1d1b65f7c32f2a86a9f@...kaller.appspotmail.com
> Fixes: 9c94bbf9a87b ("xdp: recycle Page Pool backed skbs built from XDP frames")
>
> BUG: kernel NULL pointer dereference, address: 0000000000000d28
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0002) - not-present page
> PGD 7b741067 P4D 7b741067 PUD 7c1ca067 PMD 0
> Oops: 0002 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 5080 Comm: syz-executor371 Not tainted 6.2.0-syzkaller-13030-g3c2611bac08a #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
> RIP: 0010:memset_erms+0xd/0x20 arch/x86/lib/memset_64.S:66
> Code: 01 48 0f af c6 f3 48 ab 89 d1 f3 aa 4c 89 c8 c3 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 66 0f 1f 00 49 89 f9 40 88 f0 48 89 d1 <f3> aa 4c 89 c8 c3 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 66 0f 1f
> RSP: 0018:ffffc90003baf730 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff888028b94000 RCX: 0000000000000020
> RDX: 0000000000000020 RSI: 0000000000000000 RDI: 0000000000000d28
> RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000d28
> R10: ffffed100517281c R11: 0000000000094001 R12: 0000000000000d48
> R13: 0000000000000d28 R14: 0000000000000f68 R15: 0000000000000100
> FS: 0000555555979300(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000d28 CR3: 0000000028e2d000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> __finalize_skb_around net/core/skbuff.c:321 [inline]
> __build_skb_around+0x232/0x3a0 net/core/skbuff.c:379
> build_skb_around+0x32/0x290 net/core/skbuff.c:444
> __xdp_build_skb_from_frame+0x121/0x760 net/core/xdp.c:622
> xdp_recv_frames net/bpf/test_run.c:248 [inline]
> xdp_test_run_batch net/bpf/test_run.c:334 [inline]
> bpf_test_run_xdp_live+0x1289/0x1930 net/bpf/test_run.c:362
> bpf_prog_test_run_xdp+0xa05/0x14e0 net/bpf/test_run.c:1418
> bpf_prog_test_run kernel/bpf/syscall.c:3675 [inline]
> __sys_bpf+0x1598/0x5100 kernel/bpf/syscall.c:5028
> __do_sys_bpf kernel/bpf/syscall.c:5114 [inline]
> __se_sys_bpf kernel/bpf/syscall.c:5112 [inline]
> __x64_sys_bpf+0x79/0xc0 kernel/bpf/syscall.c:5112
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f320b4efca9
> 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:00007ffd2c9924d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f320b4efca9
> RDX: 0000000000000048 RSI: 0000000020000080 RDI: 000000000000000a
> RBP: 00007f320b4b3e50 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f320b4b3ee0
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> </TASK>
> Modules linked in:
> CR2: 0000000000000d28
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:memset_erms+0xd/0x20 arch/x86/lib/memset_64.S:66
> Code: 01 48 0f af c6 f3 48 ab 89 d1 f3 aa 4c 89 c8 c3 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 66 0f 1f 00 49 89 f9 40 88 f0 48 89 d1 <f3> aa 4c 89 c8 c3 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 66 0f 1f
> RSP: 0018:ffffc90003baf730 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff888028b94000 RCX: 0000000000000020
> RDX: 0000000000000020 RSI: 0000000000000000 RDI: 0000000000000d28
> RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000d28
> R10: ffffed100517281c R11: 0000000000094001 R12: 0000000000000d48
> R13: 0000000000000d28 R14: 0000000000000f68 R15: 0000000000000100
> FS: 0000555555979300(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000d28 CR3: 0000000028e2d000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess), 1 bytes skipped:
> 0: 48 0f af c6 imul %rsi,%rax
> 4: f3 48 ab rep stos %rax,%es:(%rdi)
> 7: 89 d1 mov %edx,%ecx
> 9: f3 aa rep stos %al,%es:(%rdi)
> b: 4c 89 c8 mov %r9,%rax
> e: c3 retq
> f: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> 16: 00 00 00 00
> 1a: 66 90 xchg %ax,%ax
> 1c: 66 0f 1f 00 nopw (%rax)
> 20: 49 89 f9 mov %rdi,%r9
> 23: 40 88 f0 mov %sil,%al
> 26: 48 89 d1 mov %rdx,%rcx
> * 29: f3 aa rep stos %al,%es:(%rdi) <-- trapping instruction
Looks like skb_shinfo() returns %NULL inside __finalize_skb_around(). My
code didn't touch this at all, but I'm digging this already anyway :s
+ Toke, test_run author :p
> 2b: 4c 89 c8 mov %r9,%rax
> 2e: c3 retq
> 2f: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> 36: 00 00 00 00
> 3a: 66 90 xchg %ax,%ax
> 3c: 66 data16
> 3d: 0f .byte 0xf
> 3e: 1f (bad)
>
>
> ---
> 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
Thanks,
Olek
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