Re: redirect stdout and stderr to different file under sandboxing in linux

[Bhuvan Gupta <bhuvangu@xxxxxxxxx>]

Running following command gives the below AVC

>>>sandbox ./a.out 2>err 

SELinux is preventing /a.out from write access on the file .

*****  Plugin leaks (86.2 confidence) suggests   *****************************

If you want to ignore a.out trying to write access the  file, because you believe it should not need this access.

Then you should report this as a bug.  

You can generate a local policy module to dontaudit this access.

Do

# grep /a.out /var/log/audit/audit.log | audit2allow -D -M mypol

# semodule -i mypol.pp

*****  Plugin catchall (14.7 confidence) suggests   **************************

If you believe that a.out should be allowed write access on the  file by default.

Then you should report this as a bug.

You can generate a local policy module to allow this access.

Do

allow this access for now by executing:

# grep a.out /var/log/audit/audit.log | audit2allow -M mypol

# semodule -i mypol.pp

Additional Information:

Source Context                unconfined_u:unconfined_r:sandbox_t:s0:c296,c597

Target Context                unconfined_u:object_r:etc_runtime_t:s0

Target Objects                 [ file ]

Source                        a.out

Source Path                   /a.out

Port                          <Unknown>

Host                          localhost.localdomain

Source RPM Packages           

Target RPM Packages           

Policy RPM                    selinux-policy-3.13.1-23.el7.noarch

Selinux Enabled               True

Policy Type                   targeted

Enforcing Mode                Enforcing

Host Name                     localhost.localdomain

Platform                      Linux localhost.localdomain 3.10.0-121.el7.x86_64

                              #1 SMP Tue Apr 8 10:48:19 EDT 2014 x86_64 x86_64

Alert Count                   1

First Seen                    2015-05-28 23:11:59 IST

Last Seen                     2015-05-28 23:11:59 IST

Local ID                      cd5a2639-5a52-4b0f-95e1-bf3d3c965dd4

Raw Audit Messages

type=AVC msg=audit(1432834919.99:391): avc:  denied  { write } for  pid=2626 comm="a.out" path="/err" dev="dm-0" ino=736779 scontext=unconfined_u:unconfined_r:sandbox_t:s0:c296,c597 tcontext=unconfined_u:object_r:etc_runtime_t:s0 tclass=file

type=SYSCALL msg=audit(1432834919.99:391): arch=x86_64 syscall=execve success=yes exit=0 a0=330a3f0 a1=330eaa0 a2=7fff6a67fe50 a3=7fff6a67e840 items=0 ppid=2625 pid=2626 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts0 ses=1 comm=a.out exe=/a.out subj=unconfined_u:unconfined_r:sandbox_t:s0:c296,c597 key=(null)

Hash: a.out,sandbox_t,etc_runtime_t,file,write

Thanks

Bhuvan

On Thu, May 28, 2015 at 3:53 PM, Daniel J Walsh <dwalsh@xxxxxxxxxx> wrote:

What AVC's are you seeing?

audit2allow -la

On 05/23/2015 07:19 AM, Bhuvan Gupta wrote:

MORE INFO

content of Test.cpp

#include<stdio>

 int main(void) {

  fprintf(stderr,"error/n");

  return 0;

 }

compile it and now

./a.out 

print error to console

./a.out 2> err

print to err file

sandbox ./a.out 2>err

nothing gets printed on console or in err file.

Is sandbox is eating it up ?

Thanks

Bhuvan

On Sat, May 23, 2015 at 4:02 PM, Bhuvan Gupta <bhuvangu@xxxxxxxxx> wrote:

EXTRA INFO:

even if i run 

sandbox ./a.out

Even then it doesnt print floating point error on console

On Sat, May 23, 2015 at 3:40 PM, Bhuvan Gupta <bhuvangu@xxxxxxxxx> wrote:

Hello All,

I have an Test.cpp which is run under sandbox(RHEL7):

Test.cpp content:

#include<stdio>

 int main(void) {

  int a = 1/0;

  return 0;

 }

compile it using gcc(4.8) Test.cpp which produces the a.out

Now running a.out prints floating pointing exception on console

Now i thought that if i redirect stderr to a file, i expect the error to be printed in file.

But that is not the case it still continue to print in console.

Googling reveal that under such exception the program is terminated immediately and if you capture the stderr of bash then it should redirect.

So i run

su -c ./a.out 2>err 

Bingo error get printed in err file.

Now the MAIN GAME STARTS

i want to run it under sandbox 

so i run:

su -c 'sandbox ./a.out 1>out 2>err'

But there is nothing printed in err file or in console.

How to capture stdout and stderr under such situation ?

Thanks

Bhuvan

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