Re: [syzbot] [bpf?] KMSAN: uninit-value in bpf_bprintf_prepare

[Martin KaFai Lau]

On 2/21/24 12:55 PM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    c1ca10ceffbb Merge tag 'scsi-fixes' of git://git.kernel.or..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1364db0c180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e3dd779fba027968
> dashboard link: https://syzkaller.appspot.com/bug?extid=c2dc95f7d0825a145992
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/83d019f0ac47/disk-c1ca10ce.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/49e05dd7a23d/vmlinux-c1ca10ce.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/68ec9fa2d33d/bzImage-c1ca10ce.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+c2dc95f7d0825a145992@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> =====================================================
> BUG: KMSAN: uninit-value in bpf_bprintf_prepare+0x20d7/0x23b0 kernel/bpf/helpers.c:904
>   bpf_bprintf_prepare+0x20d7/0x23b0 kernel/bpf/helpers.c:904
>   ____bpf_snprintf kernel/bpf/helpers.c:1060 [inline]
>   bpf_snprintf+0x141/0x360 kernel/bpf/helpers.c:1044
>   ___bpf_prog_run+0x2180/0xdb80 kernel/bpf/core.c:1986
>   __bpf_prog_run288+0xb5/0xe0 kernel/bpf/core.c:2226

#syz dup: [syzbot] [bpf?] [net?] KMSAN: uninit-value in dev_map_lookup_elem

>   bpf_dispatcher_nop_func include/linux/bpf.h:1231 [inline]
>   __bpf_prog_run include/linux/filter.h:651 [inline]
>   bpf_prog_run include/linux/filter.h:658 [inline]
>   bpf_prog_run_pin_on_cpu include/linux/filter.h:675 [inline]
>   bpf_flow_dissect+0x127/0x470 net/core/flow_dissector.c:991
>   bpf_prog_test_run_flow_dissector+0x6f4/0xa20 net/bpf/test_run.c:1359
>   bpf_prog_test_run+0x6af/0xac0 kernel/bpf/syscall.c:4107
>   __sys_bpf+0x649/0xd60 kernel/bpf/syscall.c:5475
>   __do_sys_bpf kernel/bpf/syscall.c:5561 [inline]
>   __se_sys_bpf kernel/bpf/syscall.c:5559 [inline]
>   __x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5559
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
>   entry_SYSCALL_64_after_hwframe+0x63/0x6b
>
> Local variable stack created at:
>   __bpf_prog_run288+0x45/0xe0 kernel/bpf/core.c:2226
>   bpf_dispatcher_nop_func include/linux/bpf.h:1231 [inline]
>   __bpf_prog_run include/linux/filter.h:651 [inline]
>   bpf_prog_run include/linux/filter.h:658 [inline]
>   bpf_prog_run_pin_on_cpu include/linux/filter.h:675 [inline]
>   bpf_flow_dissect+0x127/0x470 net/core/flow_dissector.c:991
>
> CPU: 0 PID: 6318 Comm: syz-executor.2 Not tainted 6.8.0-rc4-syzkaller-00331-gc1ca10ceffbb #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
> =====================================================