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

From: Mark Rutland
Date: Tue Sep 11 2018 - 08:16:12 EST

On Tue, Sep 11, 2018 at 02:48:15AM +0100, Dmitry Safonov wrote:
> Hi all,


> 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@xxxxxxx>

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.


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))