netdev - Re: [PATCH] slip: Fix use-after-free Read in slip

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Date:   Wed, 27 Nov 2019 07:27:30 +0100
From:   Lukas Bulwahn <lukas.bulwahn@...il.com>
To:     Jouni Högander <jouni.hogander@...kie.com>
Cc:     netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
        Oliver Hartkopp <socketcan@...tkopp.net>
Subject: Re: [PATCH] slip: Fix use-after-free Read in slip_open

On Mon, Nov 25, 2019 at 1:28 PM Jouni Högander
<jouni.hogander@...kie.com> wrote:
>
> jouni.hogander@...kie.com writes:
>
> > From: Jouni Hogander <jouni.hogander@...kie.com>
> >
> > Slip_open doesn't clean-up device which registration failed from the
> > slip_devs device list. On next open after failure this list is iterated
> > and freed device is accessed. Fix this by calling sl_free_netdev in error
> > path.
> >
> > Here is the trace from the Syzbot:
> >
> > __dump_stack lib/dump_stack.c:77 [inline]
> > dump_stack+0x197/0x210 lib/dump_stack.c:118
> > print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
> > __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
> > kasan_report+0x12/0x20 mm/kasan/common.c:634
> > __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
> > sl_sync drivers/net/slip/slip.c:725 [inline]
> > slip_open+0xecd/0x11b7 drivers/net/slip/slip.c:801
> > tty_ldisc_open.isra.0+0xa3/0x110 drivers/tty/tty_ldisc.c:469
> > tty_set_ldisc+0x30e/0x6b0 drivers/tty/tty_ldisc.c:596
> > tiocsetd drivers/tty/tty_io.c:2334 [inline]
> > tty_ioctl+0xe8d/0x14f0 drivers/tty/tty_io.c:2594
> > vfs_ioctl fs/ioctl.c:46 [inline]
> > file_ioctl fs/ioctl.c:509 [inline]
> > do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
> > ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
> > __do_sys_ioctl fs/ioctl.c:720 [inline]
> > __se_sys_ioctl fs/ioctl.c:718 [inline]
> > __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
> > do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > Fixes: 3b5a39979daf ("slip: Fix memory leak in slip_open error path")
> > Reported-by: syzbot+4d5170758f3762109542@...kaller.appspotmail.com
>
> Unfortunately I'm not able to reproduce this by myself. But to my
> understanding scenario described above is possible path to this
> use-after-free bug.
>

As slcan copies some parts from slip, would this use-after-free bug
also occur with the sclan_open function?

The err_free_chan error path in slcan_open does exactly the same as in
slip, so would we also need to add sl_free_netdev(sl->dev) there,
right?

Jouni, could you submit an additional patch to slcan?


Lukas