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Date: Tue, 8 Jan 2019 19:34:24 +0400
From: Entropy Moe <3ntr0py1337@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: security@...nel.org, oss-security@...ts.openwall.com
Subject: Re: Linux Kernel 4.20(21) deadlock vulnerability.

Hello Greg,
thank you for reply,
I have have them tested on the new kernel 5

On Tue, Jan 8, 2019 at 7:26 PM Greg KH <gregkh@...uxfoundation.org> wrote:

> On Tue, Jan 08, 2019 at 07:08:14PM +0400, Entropy Moe wrote:
> > Hello,
> > I wanted to let you know that there seem to be a deadlock vulnerability
> on
> > the linux kernel 4.20.
> > I am attaching the result report from syzkaller which also got the c code
> > for replication.
> >
> > thank you,
>
> > Syzkaller hit 'possible deadlock in console_unlock' bug.
> >
> > RBP: 00000000006cb018 R08: 0000000000000001 R09: 0000000000000031
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
> > R13: ffffffffffffffff R14: 0000000000000000 R15: 0000000000000000
> >
> > ======================================================
> > WARNING: possible circular locking dependency detected
> > 4.20.0-rc7+ #8 Not tainted
> > ------------------------------------------------------
> > syz-executor579/2028 is trying to acquire lock:
> > 00000000e478796d (console_owner){-.-.}, at: log_next
> kernel/printk/printk.c:489 [inline]
> > 00000000e478796d (console_owner){-.-.}, at: console_unlock+0x33d/0xd30
> kernel/printk/printk.c:2401
> >
> > but task is already holding lock:
> > 0000000030388923 (&(&port->lock)->rlock){-.-.}, at: pty_write+0xcd/0x1d0
> drivers/tty/pty.c:120
> >
> > which lock already depends on the new lock.
>
>
> Are you sure this is a real problem?  Can you deadlock this when
> running?
>
> Also, try 5.0-rc1, a number of tty core changes went in there to try to
> resolve these types of issues.  They have not been backported to 4.20.y
> yet as they need to get more testing.  If you could run your same test
> suite on that kernel, it would be great to find out your results.
>
> thanks,
>
> greg k-h
>

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