Subject: Re: [syzbot] WARNING in bpf_verifier_vlog

From: [email-masked]
Date: Fri, 9 Sep 2022 09:37:00 -0700

On 09/08, syzbot wrote:
> Hello,

> syzbot found the following issue on:

> HEAD commit:    7e18e42e4b28 Linux 6.0-rc4
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1551da55080000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f4d613baa509128c
> dashboard link:  
> https://syzkaller.appspot.com/bug?extid=8b2a08dfbd25fd933d75
> 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=1798cab7080000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16ccbdc5080000

> Downloadable assets:
> disk image:  
> https://storage.googleapis.com/syzbot-assets/da260c675b46/disk-7e18e42e.raw.xz
> vmlinux:  
> https://storage.googleapis.com/syzbot-assets/58f7bbbaa6ff/vmlinux-7e18e42e.xz

> IMPORTANT: if you fix the issue, please add the following tag to the  
> commit:
> Reported-by: [email-masked]

> ------------[ cut here ]------------
> verifier log line truncated - local buffer too short
> WARNING: CPU: 1 PID: 3604 at kernel/bpf/verifier.c:300  
> bpf_verifier_vlog+0x267/0x3c0 kernel/bpf/verifier.c:300
> Modules linked in:
> CPU: 1 PID: 3604 Comm: syz-executor146 Not tainted 6.0.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
> Google 08/26/2022
> RIP: 0010:bpf_verifier_vlog+0x267/0x3c0 kernel/bpf/verifier.c:300
> Code: f5 95 3d 0c 31 ff 89 ee e8 06 07 f0 ff 40 84 ed 75 1a e8 7c 0a f0  
> ff 48 c7 c7 c0 e7 f3 89 c6 05 d4 95 3d 0c 01 e8 fb 4c ae 07 <0f> 0b e8 62  
> 0a f0 ff 48 89 da 48 b8 00 00 00 00 00 fc ff df 48 c1
> RSP: 0018:ffffc900039bf8a0 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: ffff888017a19210 RCX: 0000000000000000
> RDX: ffff888021fb1d80 RSI: ffffffff8161f408 RDI: fffff52000737f06
> RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000080000000 R11: 0000000000000000 R12: ffffffff89f5aba0
> R13: 00000000000003ff R14: ffff888017a19214 R15: ffff888012705800
> FS:  0000555555cba300(0000) GS:ffff8880b9b00000(0000)  
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020100000 CR3: 000000001bf9e000 CR4: 0000000000350ee0
> Call Trace:
>   <TASK>
>   __btf_verifier_log+0xbb/0xf0 kernel/bpf/btf.c:1375
>   __btf_verifier_log_type+0x451/0x8f0 kernel/bpf/btf.c:1413
>   btf_func_proto_check_meta+0x117/0x160 kernel/bpf/btf.c:3905
>   btf_check_meta kernel/bpf/btf.c:4588 [inline]
>   btf_check_all_metas+0x3c1/0xa70 kernel/bpf/btf.c:4612
>   btf_parse_type_sec kernel/bpf/btf.c:4748 [inline]

Benjamin, this seems to be coming from BTF loading. Could this be caused
by some of your recent activity with things like:

commit f9b348185f4d684cc19e6bd9b87904823d5aa5ed
Author: Benjamin Tissoires <[email-masked]>
Date:   Tue Sep 6 17:13:01 2022 +0200

     bpf/btf: bump BTF_KFUNC_SET_MAX_CNT

?

I haven't looked too deep, maybe you can give it a shot? There is
reproducer; should be relatively easy to verify. Thx.

>   btf_parse kernel/bpf/btf.c:5031 [inline]
>   btf_new_fd+0x939/0x1e70 kernel/bpf/btf.c:6710
>   bpf_btf_load kernel/bpf/syscall.c:4314 [inline]
>   __sys_bpf+0x13bd/0x6130 kernel/bpf/syscall.c:4998
>   __do_sys_bpf kernel/bpf/syscall.c:5057 [inline]
>   __se_sys_bpf kernel/bpf/syscall.c:5055 [inline]
>   __x64_sys_bpf+0x75/0xb0 kernel/bpf/syscall.c:5055
>   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+0x63/0xcd
> RIP: 0033:0x7fb092221c29
> 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:00007fff5b0a6878 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fb092221c29
> RDX: 0000000000000020 RSI: 0000000020000240 RDI: 0000000000000012
> RBP: 00007fb0921e5dd0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb0921e5e60
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>   </TASK>

> ---
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