Re: UBSAN: array-index-out-of-bounds in decode_data

Marco Elver
2021-01-22T07:25:01Z

On Thu, 21 Jan 2021 at 19:30, syzbot
<syzbot+70ba6cae2f44c82dcb76@syzkaller.appspotmail.com> wrote:
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 9791581c Merge tag 'for-5.11-rc4-tag' of git://git.kernel...
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13cd09a4d00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=39701af622f054a9
> dashboard link: https://syzkaller.appspot.com/bug?extid=70ba6cae2f44c82dcb76
> compiler: gcc (GCC) 10.1.0-syz 20200507
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=133d8030d00000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+70ba6cae2f44c82dcb76@syzkaller.appspotmail.com
>
> ================================================================================
> UBSAN: array-index-out-of-bounds in drivers/net/hamradio/6pack.c:845:16
> index 400 is out of range for type 'unsigned char [400]'
> CPU: 1 PID: 8 Comm: kworker/u4:0 Not tainted 5.11.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: events_unbound flush_to_ldisc
> Call Trace:
> __dump_stack lib/dump_stack.c:79 [inline]
> dump_stack+0x107/0x163 lib/dump_stack.c:120
> ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
> __ubsan_handle_out_of_bounds.cold+0x62/0x6c lib/ubsan.c:356
> decode_data.part.0+0x2c8/0x2e0 drivers/net/hamradio/6pack.c:845

It looks like this might be due to a race condition; syzbot had
detected a data race in this code a while back, but it seems this was
never fixed: https://lore.kernel.org/lkml/000000000000bbb17d05a19540cd@google.com/

> decode_data drivers/net/hamradio/6pack.c:965 [inline]
> sixpack_decode drivers/net/hamradio/6pack.c:968 [inline]
> sixpack_receive_buf drivers/net/hamradio/6pack.c:458 [inline]
> sixpack_receive_buf+0xd8c/0x1320 drivers/net/hamradio/6pack.c:435
> tty_ldisc_receive_buf+0x14a/0x190 drivers/tty/tty_buffer.c:465
> tty_port_default_receive_buf+0x6e/0xa0 drivers/tty/tty_port.c:38
> receive_buf drivers/tty/tty_buffer.c:481 [inline]
> flush_to_ldisc+0x20d/0x380 drivers/tty/tty_buffer.c:533
> process_one_work+0x98d/0x15f0 kernel/workqueue.c:2275
> worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
> kthread+0x3b1/0x4a0 kernel/kthread.c:292
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
> ================================================================================

Thanks,
-- Marco