Re: [PATCHv3 0/6] tty: Hold write ldisc sem in tty_reopen()

Dmitry Safonov
2018-09-11T12:43:01Z

On Tue, 2018-09-11 at 13:16 +0100, Mark Rutland wrote:
> On Tue, Sep 11, 2018 at 02:48:15AM +0100, Dmitry Safonov wrote:
> > Hi all,
>
> Hi,
>
> > Three fixes that worth to have in the @stable, as we've hit them on
> > v4.9
> > stable.
> >
> > And for linux-next - adding lockdep asserts for line discipline
> > changing
> > code, verifying that write ldisc sem will be held forthwith.
> >
> > The last patch is optional and probably, timeout can be dropped for
> > read_lock(). I'll do it if everyone agrees.
> >
> > Rong Chen, could you kindly re-run this version to see if the
> > lockup
> > from v1 still happens? I wasn't able to reproduce it..
>
> These patches seem to fix issues I've been seeing on arm64 for a
> while
> but hadn't managed to track down.
>
> For patches 1, 3, and 5, feel free to add:
>
> Tested-by: Mark Rutland <mark.rutland@arm.com>

Thanks, Mark!
Will add on the next version.

>
> On vanilla v4.19-rc2, the below reproducer would fire in seconds,
> whereas with those patches applied, I have not seen issues after 10s
> of
> minutes of testing.
>
> Thanks,
> Mark.
>
> Syzkaller hit 'KASAN: user-memory-access Write in n_tty_set_termios'
> bug.
>
> IPv6: ADDRCONF(NETDEV_UP): veth0: link is not ready
> ipV6: ADDRCONF(NETDEV_UP): veth1: link is not ready
> IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
> IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
> ==================================================================
> BUG: KASAN: user-memory-access in memset include/linux/string.h:330
> [inline]
> BUG: KASAN: user-memory-access in bitmap_zero
> include/linux/bitmap.h:216 [inline]
> BUG: KASAN: user-memory-access in n_tty_set_termios+0xe4/0xd08
> drivers/tty/n_tty.c:1784
> Write of size 512 at addr 0000000000001060 by task syz-executor0/3007
>
> CPU: 1 PID: 3007 Comm: syz-executor0 Not tainted 4.19.0-rc2-dirty #4
> Hardware name: linux,dummy-virt (DT)
> Call trace:
> dump_backtrace+0x0/0x340 arch/arm64/include/asm/ptrace.h:270
> show_stack+0x20/0x30 arch/arm64/kernel/traps.c:152
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0xec/0x150 lib/dump_stack.c:113
> kasan_report_error mm/kasan/report.c:352 [inline]
> kasan_report+0x228/0x360 mm/kasan/report.c:412
> check_memory_region_inline mm/kasan/kasan.c:253 [inline]
> check_memory_region+0x114/0x1c8 mm/kasan/kasan.c:267
> memset+0x2c/0x50 mm/kasan/kasan.c:285
> memset include/linux/string.h:330 [inline]
> bitmap_zero include/linux/bitmap.h:216 [inline]
> n_tty_set_termios+0xe4/0xd08 drivers/tty/n_tty.c:1784
> tty_set_termios+0x538/0x760 drivers/tty/tty_ioctl.c:341
> set_termios+0x348/0x968 drivers/tty/tty_ioctl.c:414
> tty_mode_ioctl+0x8f0/0xc60 drivers/tty/tty_ioctl.c:779
> n_tty_ioctl_helper+0x6c/0x390 drivers/tty/tty_ioctl.c:940
> n_tty_ioctl+0x6c/0x490 drivers/tty/n_tty.c:2450
> tty_ioctl+0x610/0x19a8 drivers/tty/tty_io.c:2655
> vfs_ioctl fs/ioctl.c:46 [inline]
> file_ioctl fs/ioctl.c:501 [inline]
> do_vfs_ioctl+0x1bc/0x1618 fs/ioctl.c:685
> ksys_ioctl+0xbc/0x108 fs/ioctl.c:702
> __do_sys_ioctl fs/ioctl.c:709 [inline]
> __se_sys_ioctl fs/ioctl.c:707 [inline]
> __arm64_sys_ioctl+0x6c/0xa0 fs/ioctl.c:707
> __invoke_syscall arch/arm64/kernel/syscall.c:36 [inline]
> invoke_syscall arch/arm64/kernel/syscall.c:48 [inline]
> el0_svc_common+0x150/0x288 arch/arm64/kernel/syscall.c:84
> el0_svc_handler+0x54/0xf0 arch/arm64/kernel/syscall.c:130
> el0_svc+0x8/0xc arch/arm64/kernel/entry.S:917
> ==================================================================
>
>
> Syzkaller reproducer:
> # {Threaded:true Collide:true Repeat:true RepeatTimes:0 Procs:1
> Sandbox:none Fault:false FaultCall:-1 FaultNth:0 EnableTun:true
> UseTmpDir:true EnableCgroups:true EnableNetdev:true ResetNet:true
> HandleSegv:true Repro:false Trace:false}
> r0 = openat$ptmx(0xffffffffffffff9c,
> &(0x7f0000000000)='/dev/ptmx\x00', 0x0, 0x0)
> ioctl$TIOCGPTPEER(r0, 0x40045431, 0x6e0000)
> r1 = syz_open_pts(r0, 0x0)
> ioctl$TCXONC(r1, 0x5437, 0x0)
> ioctl$TIOCGSOFTCAR(r0, 0x5419, &(0x7f00000000c0))
> r2 = semget(0x0, 0x1, 0x1a)
> semctl$IPC_INFO(r2, 0x0, 0x3, &(0x7f0000000100)=""/166)
> syz_open_pts(r0, 0x2)
> ioctl$TCSETAW(r0, 0x5407, &(0x7f0000000080))
>

--
Thanks,
Dmitry