On Thu, Jan 10, 2013 at 3:24 PM, Michael Kerrisk (man-pages)
<mtk.manpages@xxxxxxxxx> wrote:
> [CC+=Pavel]
>
> Hi Kees,
>
> On Thu, Jan 10, 2013 at 10:28 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>> This documents the Yama LSM's prctl handler that allows processes to
>> declare ptrace restriction exception relationships via PR_SET_PTRACER.
>
> This is synchronicity! I was just looking at what was undocumented in
> prctl() after a conversation with Pavel and wondering about pinging
> you about PR_SET_PTRACER.
Ah-ha! Great. :)
> Some questions/observations:
>
> 1. From the look of it, each tracee can have only one tracer, so that
> PR_SET_PTRACER overwrites any previous PID, right. The text implies
> that, but I'll add a few more words to make it explicit.
Yes, that's correct. There is only one at a time.
> 2. There is no PR_GET_PTRACER operation. I suppose it's not needed for
> your purposes. I wonder however if it might matter for CRIU to have
> PR_GET_PTRACER, hence I CC Pavel.
No one has wanted it, but it should be trivial to add it.
> Your patch is applied.
Thanks!
-Kees
>
> Cheers,
>
> Michael
>
>> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>> ---
>> man2/prctl.2 | 18 +++++++++++++++++-
>> 1 file changed, 17 insertions(+), 1 deletion(-)
>>
>> diff --git a/man2/prctl.2 b/man2/prctl.2
>> index c8a4919..506c7b3 100644
>> --- a/man2/prctl.2
>> +++ b/man2/prctl.2
>> @@ -45,9 +45,10 @@
>> .\" 2012-09-20 Kees Cook, document PR_SET_NO_NEW_PRIVS, PR_GET_NO_NEW_PRIVS
>> .\" 2012-10-25 Michael Kerrisk, Document PR_SET_TIMERSLACK and
>> .\" PR_GET_TIMERSLACK
>> +.\" 2013-01-10 Kees Cook, document PR_SET_PTRACER
>> .\"
>> .\"
>> -.TH PRCTL 2 2012-10-25 "Linux" "Linux Programmer's Manual"
>> +.TH PRCTL 2 2013-01-10 "Linux" "Linux Programmer's Manual"
>> .SH NAME
>> prctl \- operations on a process
>> .SH SYNOPSIS
>> @@ -270,6 +271,21 @@ Return the current value of the parent process death signal,
>> in the location pointed to by
>> .IR "(int\ *) arg2" .
>> .TP
>> +.BR PR_SET_PTRACER " (since Linux 3.4)"
>> +This is only meaningful when the Yama LSM is enabled and in mode 1
>> +("restricted ptrace", visible via
>> +.IR /proc/sys/kernel/yama/ptrace_scope ).
>> +When a "ptracer process id" is passed in \fIarg2\fP, the caller is declaring
>> +that the ptracer process can ptrace the current process as if it were a
>> +direct process ancestor. When set to 0, this relationship is removed. When
>> +set to
>> +.BR PR_SET_PTRACER_ANY,
>> +the ptrace restrictions introduced by Yama are effectively disabled for the
>> +current process.
>> +
>> +For further information, see the kernel source file
>> +.IR Documentation/security/Yama.txt .
>> +.TP
>> .BR PR_SET_SECCOMP " (since Linux 2.6.23)"
>> .\" See http://thread.gmane.org/gmane.linux.kernel/542632
>> .\" [PATCH 0 of 2] seccomp updates
>> --
>> 1.7.9.5
>>
>> --
>> Kees Cook
>> Chrome OS Security
>
>
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Author of "The Linux Programming Interface"; http://man7.org/tlpi/
--
Kees Cook
Chrome OS Security
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