Re: [syzbot] unexpected kernel reboot (4)

[Andrey Konovalov]

On Wed, Apr 14, 2021 at 7:45 AM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>
> On Tue, Apr 13, 2021 at 11:27 PM syzbot
> <syzbot+9ce030d4c89856b27619@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    89698bec Merge tag 'm68knommu-for-v5.12-rc7' of git://git...
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1243fcfed00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=b234ddbbe2953747
> > dashboard link: https://syzkaller.appspot.com/bug?extid=9ce030d4c89856b27619
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=173e92fed00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1735da2ed00000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+9ce030d4c89856b27619@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > output_len: 0x000000000e74eb68
> > kernel_total_size: 0x000000000f226000
> > needed_size: 0x000000000f400000
> > trampoline_32bit: 0x000000000009d000
> > Decompressing Linux... Parsing ELF... done.
> > Booting the kernel.
>
> +linux-input
>
> The reproducer connects some USB HID device and communicates with the driver.
> Previously we observed reboots because HID devices can trigger reboot
> SYSRQ, but we disable it with "CONFIG_MAGIC_SYSRQ is not set".
> How else can a USB device reboot the machine? Is it possible to disable it?
> I don't see any direct includes of <linux/reboot.h> in drivers/usb/*

This happens when a keyboard sends the Ctrl+Alt+Del sequence, see
fn_boot_it()->ctrl_alt_del() in drivers/tty/vt/keyboard.c.

There was a patchset by Tetsuo [1] to suppress this, but I think it
was abandoned.

(This reminds of a somewhat related syzkaller issue:
https://github.com/google/syzkaller/issues/1824; it relies on a
similar reproducer.)

[1] https://groups.google.com/g/syzkaller/c/7wCmrGlLgm0/m/5yG6HVtbBQAJ