Bug#854009: soundmodem: starts kiss device with incorrect permissions
Morning,
That sounds like a sensible approach, yes!
In my earlier investigation I'd done some work with dialout but then
pushed it to the back of my mind!
I think dialout is an easier group to deal with for those of us who are
using hardware TNCs also - it means everything is caught by the same
group. I don't much fancy writing udev rules to catch every TNC when we
can just treat them like a serial port.
Regards,
Dave
--
Hibby
d@vehibberd.com
On Fri, 3 Feb 2017, at 07:49 AM, Thomas Osterried wrote:
> Hello,
>
> I'd like to argue that this is not the right approach.
>
> group tty's default permissions are 0620.
> That is so, in order to allow programs like write(1) or wall(1) writing
> to the
> users terminal. These programs are set-gid-bit tty.
> For soundmodem, those programs also should not be allowed to write to
> /dev/soundmodem. Thus considered, not 0660 as suggested, but 0600 should
> be the correct permission.
>
> The patch suggests to add a user who's allowed operate with soundmodem
> to the group tty. This would lead to an security risk by design, because
> a normal user is user now able to read devices like /dev/vcs (virtual
> console
> memory / screen dump).
>
> The correct and non-harmful ownership would be the group "dialout", and
> then ok
> with permission 0660. That goes along with the unix security design for
> modem
> access permissions for users.
> An even better approach would be a group ownership for
> ham-radio-operators
> (like ax25-apps/-tools suggest, with gid "hams" or "ax25"), but since
> there's
> no standard and no defualt group currently in /etc/group, I suppose group
> "dialout" would be sufficient.
>
> vy 73,
> - Thomas dl9sau
>
>
> On Fri, Feb 03, 2017 at 12:39:01AM +0000, Dave Hibberd wrote:
> > Package: soundmodem
> > Version: 0.20-5
> > Severity: normal
> > Tags: patch
> >
> > Dear Maintainer,
> >
> > Running soundmodem creates a kiss serial device with permissions that render it
> > inaccessible to normal users, or users in the tty group.
> >
> > Upon starting soundmodem with Channel "Packet IO" Mode set as KISS, soundmodem
> > creates a pty and a link to that file, /dev/soundmodem*.
> >
> > Normal users, and users in the tty group cannot access this device - this means
> > packet programs, such as Xastir, have to be run as root.
> >
> > Listing the file permissions of the created devices shows:
> >
> > → ls -al /dev/soundmodem0
> > lrwxrwxrwx 1 root root 10 Feb 3 00:18 /dev/soundmodem0 -> /dev/pts/6
> >
> > → ls -al /dev/pts/6
> > crw--w---- 1 root tty 136, 6 Feb 3 00:18 /dev/pts/6
> >
> > While root has rw on /dev/pts/6, group tty only has w. Applications cannot read
> > the terminal and show accessing it has failed.
> >
> > I have included a very minor patch which details a proposed fix below. The patch
> > allows members of the 'tty' group to read and write to the pty device.
> >
> > This has been committed to in the debian git server and can be viewed at:
> > https://anonscm.debian.org/cgit/pkg-hamradio/soundmodem.git/ however it can be
> > discarded as per maintainer's choice.
> >
> >
> > Descriptions: Allow group to read/write the created pty
> > Author: Dave Hibberd <d@vehibberd.com>
> > Last-Updated: 2017-02-24
> >
> > --- a/soundcard/kisspkt.c
> > +++ b/soundcard/kisspkt.c
> > @@ -758,7 +758,7 @@
> > tm.c_cflag = CS8 | CREAD | CLOCAL;
> > if (tcsetattr(slave, TCSANOW, &tm))
> > logerr(MLOG_FATAL, "slave: tcsetattr");
> > - //fchmod(slave, 0600);
> > + fchmod(slave, 0660);
> > if (dounlink)
> > unlink(file);
> > if (symlink(ttyname, file))
> >
> >
> > -- System Information:
> > Debian Release: 9.0
> > APT prefers testing
> > APT policy: (500, 'testing')
> > Architecture: amd64 (x86_64)
> > Foreign Architectures: i386
> >
> > Kernel: Linux 4.8.0-2-amd64 (SMP w/8 CPU cores)
> > Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
> > Shell: /bin/sh linked to /bin/dash
> > Init: systemd (via /run/systemd/system)
> >
> > Versions of packages soundmodem depends on:
> > ii libasound2 1.1.2-1
> > ii libatk1.0-0 2.22.0-1
> > ii libaudiofile1 0.3.6-3
> > ii libc6 2.24-8
> > ii libgdk-pixbuf2.0-0 2.36.3-1
> > ii libglib2.0-0 2.50.2-2
> > ii libgtk2.0-0 2.24.31-1
> > ii libhamlib2 3.0.1-1+b1
> > ii libpango-1.0-0 1.40.3-3
> > ii libxml2 2.9.4+dfsg1-2.1
> >
> > soundmodem recommends no packages.
> >
> > soundmodem suggests no packages.
> >
> > -- Configuration Files:
> > /etc/ax25/soundmodem.conf changed:
> > <?xml version="1.0"?>
> > <modem>
> > <configuration name="UHF_Packet">
> > <chaccess txdelay="150" slottime="100" ppersist="40" fulldup="0" txtail="10"/>
> > <audio type="alsa" device="plughw:CARD=Device,DEV=0" halfdup="1" capturechannelmode="Mono"/>
> > <ptt file="/dev/ttyUSB0" hamlib_model="" hamlib_params=""/>
> > <channel name="Channel 0">
> > <mod mode="afsk" bps="1200" f0="1200" f1="2200" diffenc="1"/>
> > <demod mode="afsk" bps="1200" f0="1200" f1="2200" diffdec="1"/>
> > <pkt mode="KISS" ifname="sm0" hwaddr="MM3ZRZ-5" ip="44.131.6.35" netmask="255.255.255.224" broadcast="44.131.6.63" file="/dev/soundmodem0" unlink="1"/>
> > </channel>
> > </configuration>
> > </modem>
> >
> >
> > -- no debconf information
>
>
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