Disable tracing on FreeBSD using procctl. (OpenSSH Portable 8.8)

[Bryan Drewery]

On 10/14/2021 5:44 PM, Darren Tucker wrote:
> On Fri, 15 Oct 2021 at 10:48, mike tancsa <mike at sentex.net> wrote:
>>       With the commit below, OpenSSH portable 8.8 doesnt seem to work
>> with sftp on FreeBSD with RELENG_12 and RELENG_13.  sftp errors out with
>>
>> sftp-server[89445]: fatal: unable to make the process untraceable
> 
> As a data point,our github CI tests on FreeBSD 12 & 13 VMs and our
> test suite passes on them.  I have confirmed that both set
> HAVE_PROCCTL and that the code is being compiled in and just run a
> manual test on 13 which worked.
> 
> FreeBSD fbsd12 12.2-RELEASE-p3 FreeBSD 12.2-RELEASE-p3 GENERIC  amd64
> 
> FreeBSD fbsd13 13.0-RELEASE FreeBSD 13.0-RELEASE #0
> releng/13.0-n244733-ea31abc261f: Fri Apr  9 04:24:09 UTC 2021
> root at releng1.nyi.freebsd.org:/usr/obj/usr/src/amd64.amd64/sys/GENERIC
> amd64
> 

I think the tests may need to be improved as pid==0 represents a pseudo 
kernel process.

> #include <sys/procctl.h>                                             
> #include <err.h>                                                     
> #include <unistd.h>                                                  
>                                                                      
> int                                                                  
> main(void)                                                           
> {                                                                    
>         int disable_trace = PROC_TRACE_CTL_DISABLE;                  
>                                                                      
>         if (procctl(P_PID, getpid(), PROC_TRACE_CTL, &disable_trace))
>             err(1, "procctl");                                       
>                                                                      
>         return 0;                                                    
> }                                                                    

With 0 it runs through truss fine. (Which I don't think it should but 
I'll take that up with FreeBSD)

> procctl(P_PID,0,PROC_TRACE_CTL,0x7fffffffe478)   = 0 (0x0)


With getpid() truss gives an error since the process is already traced.

> getpid()                                         = 77976 (0x13098)     
> procctl(P_PID,77976,PROC_TRACE_CTL,0x7fffffffe478) ERR#16 'Device busy'



-- 
Bryan Drewery
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