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Date:   Thu, 28 May 2020 23:29:34 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        syzbot <syzbot+3610d489778b57cc8031@...kaller.appspotmail.com>,
        <ast@...nel.org>, <davem@...emloft.net>, <guro@...com>,
        <kuba@...nel.org>, <kuznet@....inr.ac.ru>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <syzkaller-bugs@...glegroups.com>, <yoshfuji@...ux-ipv6.org>
Subject: Re: general protection fault in inet_unhash

On 5/28/20 2:27 PM, Eric Dumazet wrote:
> 
> 
> On 5/28/20 2:01 PM, Andrii Nakryiko wrote:
>> On 5/28/20 9:44 AM, syzbot wrote:
>>> Hello,
>>>
>>> syzbot found the following crash on:
>>>
>>> HEAD commit:    dc0f3ed1 net: phy: at803x: add cable diagnostics support f..
>>> git tree:       net-next
>>> console output: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D17289cd2100000&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=sMAtpavBBjBzFzT0V8c6FcH8cu2M9da3ZozO5Lc8do0&s=t1v5ZakZM9Aw_9u_I6FbFZ28U0GFs0e9dMMUOyiDxO4&e=
>>> kernel config:  https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_.config-3Fx-3D7e1bc97341edbea6&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=sMAtpavBBjBzFzT0V8c6FcH8cu2M9da3ZozO5Lc8do0&s=yeXCTODuJF6ExmCJ-ppqMHsfvMCbCQ9zkmZi3W6NGHo&e=
>>> dashboard link: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fextid-3D3610d489778b57cc8031&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=sMAtpavBBjBzFzT0V8c6FcH8cu2M9da3ZozO5Lc8do0&s=8fAJHh81yojiinnGJzTw6hN4w4A6XRZST4463CWL9Y8&e=
>>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>>> syz repro:      https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.syz-3Fx-3D15f237aa100000&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=sMAtpavBBjBzFzT0V8c6FcH8cu2M9da3ZozO5Lc8do0&s=cPv-hQsGYs0CVz3I26BmauS0hQ8_YTWHeH5p-U5ElWY&e=
>>> C reproducer:   https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.c-3Fx-3D1553834a100000&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=sMAtpavBBjBzFzT0V8c6FcH8cu2M9da3ZozO5Lc8do0&s=r6sGJDOgosZDE9sRxqFnVibDNJFt_6IteSWeqEQLbNE&e=
>>>
>>> The bug was bisected to:
>>>
>>> commit af6eea57437a830293eab56246b6025cc7d46ee7
>>> Author: Andrii Nakryiko <andriin@...com>
>>> Date:   Mon Mar 30 02:59:58 2020 +0000
>>>
>>>       bpf: Implement bpf_link-based cgroup BPF program attachment
>>>
>>> bisection log:  https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_bisect.txt-3Fx-3D1173cd7e100000&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=sMAtpavBBjBzFzT0V8c6FcH8cu2M9da3ZozO5Lc8do0&s=rJIpYFSAMRfea3349dd7PhmLD_hriVwq8ZtTHcSagBA&e=
>>> final crash:    https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_report.txt-3Fx-3D1373cd7e100000&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=sMAtpavBBjBzFzT0V8c6FcH8cu2M9da3ZozO5Lc8do0&s=TWpx5JNdxKiKPABUScn8WB7u3fXueCp7BXwQHg4Unz0&e=
>>> console output: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D1573cd7e100000&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=sMAtpavBBjBzFzT0V8c6FcH8cu2M9da3ZozO5Lc8do0&s=-SMhn-dVZI4W51EZQ8Im0sdThgwt9M6fxUt3_bcYvk8&e=
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> Reported-by: syzbot+3610d489778b57cc8031@...kaller.appspotmail.com
>>> Fixes: af6eea57437a ("bpf: Implement bpf_link-based cgroup BPF program attachment")
>>>
>>> general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
>>> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
>>> CPU: 0 PID: 7063 Comm: syz-executor654 Not tainted 5.7.0-rc6-syzkaller #0
>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>>> RIP: 0010:inet_unhash+0x11f/0x770 net/ipv4/inet_hashtables.c:600
>>
>> No idea why it was bisected to bpf_link change. It seems completely struct sock-related. Seems like
>>
>> struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
>>
>> ends up being NULL.
>>
>> Can some more networking-savvy people help with investigating this, please?
> 
> Well, the repro definitely uses BPF

It does. Even more so, it uses bpf_link_create for cgroup which was 
added in my patch. So before it, it just won't be attaching anything. I 
just suspect that bug can be repro'ed without cgroup bpf_link and 
existed before. This particular repro, though, will always stop on my 
commit.

> 
> On the following run, my kernel does not have L2TP, so does not crash.

You'd have to use syzbot's kernel config, there is a link to it above.

> 
> [pid 817013] bpf(BPF_TASK_FD_QUERY, {task_fd_query={pid=0, fd=-1, flags=0, buf_len=7, buf="cgroup", prog_id=0, fd_type=BPF_FD_TYPE_RAW_TRACEPOINT, probe_offset=0, probe_addr=0}}, 48) = -1 ENOENT (No such file or directory)
> [pid 817013] openat(AT_FDCWD, "cgroup", O_RDWR|O_PATH) = 3
> [pid 817013] bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_CGROUP_SOCK, insn_cnt=4, insns=0x20000000, license="GPL", log_level=0, log_size=0, log_buf=NULL, kern_version=KERNEL_VERSION(0, 0, 0), prog_flags=0, prog_name="", prog_ifindex=0, expected_attach_type=BPF_CGROUP_INET_INGRESS, prog_btf_fd=-1, func_info_rec_size=8, func_info=NULL, func_info_cnt=0, line_info_rec_size=16, line_info=NULL, line_info_cnt=0, attach_btf_id=0}, 112) = -1 EPERM (Operation not permitted)
> [pid 817013] bpf(BPF_LINK_CREATE, {link_create={prog_fd=-1, target_fd=3, attach_type=BPF_CGROUP_INET_SOCK_CREATE, flags=0}}, 16) = -1 EBADF (Bad file descriptor)
> [pid 817013] socket(AF_INET, SOCK_DGRAM, IPPROTO_L2TP <unfinished ...>
> [pid 816180] <... nanosleep resumed>NULL) = 0
> [pid 816180] wait4(-1, 0x7fffa59867cc, WNOHANG|__WALL, NULL) = 0
> [pid 816180] nanosleep({tv_sec=0, tv_nsec=1000000},  <unfinished ...>
> [pid 817013] <... socket resumed>)      = -1 EPROTONOSUPPORT (Protocol not supported)
> 

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