[Toybox] ps -t is cheating.
enh
enh at google.com
Wed Oct 21 20:25:07 PDT 2015
On Wed, Oct 21, 2015 at 7:31 PM, Rob Landley <rob at landley.net> wrote:
>
>
> On 10/20/2015 12:43 AM, lamiaworks wrote:
>>
>>> Message: 1
>>> Date: Mon, 19 Oct 2015 00:09:17 -0500
>>> From: Rob Landley <rob at landley.net>
>>> To: toybox at lists.landley.net
>>> Subject: [Toybox] ps -t is cheating.
>>> Message-ID: <56247AFD.5050806 at landley.net>
>>> Content-Type: text/plain; charset=utf-8
>>>
>>> So posix says this:
>>>
>>> -t termlist
>>> Write information for processes associated with terminals given in
>>> termlist. The application shall ensure that the termlist is a single
>>> argument in the form of a <blank> or <comma>-separated list. Terminal
>>> identifiers shall be given in an implementation-defined format. [XSI]
>>> [Option Start] On XSI-conformant systems, they shall be given in one
>>> of two forms: the device's filename (for example, tty04) or, if the
>>> device's filename starts with tty, just the identifier following the
>>> characters tty (for example, "04" ). [Option End]
>>>
>>> And once again posix is somewhere back before the 1980's because
>>> pseudo-terminals do not start with "/dev/tty". In the case of linux,
>>> they've been /dev/pts/12 since, apparently, 1998.
>>>
>>> The ps man page says:
>>>
>>> -t ttylist
>>> Select by tty. This selects the processes associated with the
>>> terminals given in ttylist. Terminals (ttys, or screens for
>>> text output) can be specified in several forms: /dev/ttyS1,
>>> ttyS1, S1. A plain "-" may be used to select processes not
>>> attached to any terminal.
>>>
>>> Which is, once again, outright lying, because "-t 41" matches pts/41 but
>>> -t 5 does _not_ match tty5. You have to say "-t tty5" to get the getty
>>> instance on there.
>>
>> You just brought an old nightmare back to the surface...
>>
>> Try -t 05, if setup 'properly' you should get tty05 and that nowadays
>> should be equating to tty5's inode / character settings.
>
> $ ps -t 05
> error: TTY could not be found
>
> Linux hasn't got a /dev/tty05. It's got a /dev/tty5. But what procps's
> version of ps does (and thus what people are going to expect) is show
> pts/5 for digits.
>
> I checked in code that treats purely numeric "-t 1" as a request for
> /dev/pts/1 instead of /dev/tty1. To get tty1 say "-t tty1".
>
> I dunno about "right" behavior. I just know that posix is decades behind
> what linux is actually _doing_...
>
>> My first Mainframes (1970's) had tty0 to ttyf for systems consoles I/O
>> ONLY, and tty00 to ttyff for user terminals.
>
> That would be the decades behind part. :)
>
>> The problem was of course
>> cost for the extra user i/o cards so any tty above tty3 were often
>> assigned to users terminals and the relevant code 'fudged' to remove the
>> console level access and assign user inodes, which in turn fudged other
>> bits of code....et al...
>
> Lovely.
>
> I doubt android is providing any tty devices at all, with the possible
> exception of an adb console, just pts devices to instances of the
> "terminal" program. (Which isn't a default app on any of my phones yet,
> but I live in hope that _someday_ I won't have to install a third party
> app to get what seems to be built-in functionality.)
adb and Terminal.app both just use /dev/pts/*, yes. but Android
devices do tend to have a surprising number of /dev/tty* devices too.
here's AOSP Nexus 9, for example:
$ adb shell ls -l "/dev/tty*"
crw-rw-rw- 1 root root 5, 0 2015-10-20 07:31 /dev/tty
crw------- 1 root root 253, 0 2015-10-20 07:31 /dev/ttyFIQ0
crw------- 1 root root 238, 0 2015-10-20 07:31 /dev/ttyGS0
crw------- 1 root root 238, 1 2015-10-20 07:31 /dev/ttyGS1
crw------- 1 root root 238, 2 2015-10-20 07:31 /dev/ttyGS2
crw------- 1 root root 238, 3 2015-10-20 07:31 /dev/ttyGS3
crw------- 1 root root 238, 4 2015-10-20 07:31 /dev/ttyGS4
crw------- 1 root root 4, 64 2015-10-20 07:31 /dev/ttyS0
crw------- 1 root root 4, 65 2015-10-20 07:31 /dev/ttyS1
crw------- 1 root root 4, 66 2015-10-20 07:31 /dev/ttyS2
crw------- 1 root root 4, 67 2015-10-20 07:31 /dev/ttyS3
crw------- 1 root root 242, 0 2015-10-20 07:31 /dev/ttyTHS0
crw-rw---- 1 gps system 242, 1 2015-10-20 07:31 /dev/ttyTHS1
crw-rw---- 1 bluetooth net_bt_stack 242, 2 2015-10-20 07:31 /dev/ttyTHS2
crw------- 1 root root 242, 3 2015-10-20 07:31 /dev/ttyTHS3
> That said, the -t I checked in (yesterday?) is whitelisting specific
> names, and if the adb terminal isn't among them I need to either stop
> whitelisting (I worry that -t /dev/urandom or -t ../some/random/path
> will somehow be exploitable, even though all I'm really doing is
> stat-ing it) or add the new name...
your whitelist sounds good to me.
>>> Meanwhile procutils "ps -t pts/41" works as does "ps -t pts/../tty5"
>>> which is just _creepy_ and I'm not doing that bit. And -tty S0 is of
>>> course /dev/ttyS0 not /dev/pts/S0.
>>>
>>> I pine for a spec that means something,
>
> Which means I really should _write_ the documentation I wanted to read,
> yet again. Write a properly detailed "this is what toybox implements" as
> an actual spec in the model of posix. Then wave it at the android and
> tizen guys and have them frown and disagree with bits of it. And of
> course fill in the tests; I haven't done proper ps tests yet because the
> values change, from PIDs to %cpu output, but _how_ to do so is pretty
> straightforward. Finite list of command line options and -o selections...
>
> Alas, my open source stuff is not my day job. (I get to do some of it on
> the clock, but the past couple week's been debugging nommu toolchains
> and such...) Going as fast as I can in the time I have...
>
> Rob
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--
Elliott Hughes - http://who/enh - http://jessies.org/~enh/
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