Re: [PATCH 2/3] selinux: implement the security_uring_cmd() LSM hook

[Joel Granados <j.granados@samsung.com>]

[-- Attachment #1: Type: text/plain, Size: 5778 bytes --]

Hey Paul

On Thu, Sep 01, 2022 at 05:30:38PM -0400, Paul Moore wrote:
> On Thu, Sep 1, 2022 at 4:15 PM Joel Granados <j.granados@samsung.com> wrote:
> > Hey Paul
> >
> > I realize that you have already sent this upstream but I wanted to share
> > the Selinux part of the testing that we did to see if there is any
> > feedback.
> >
> > With my tests I see that the selinux_uring_cmd hook is run and it
> > results in a "avc : denied" when I run it with selinux in permissive
> > mode with an unpriviledged user. I assume that this is the expected
> > behavior. Here is how I tested
> >
> > *** With the patch:
> > * I ran the io_uring_passthrough.c test on a char device with an
> >   unpriviledged user.
> > * I took care of changing the permissions of /dev/ng0n1 to 666 prior
> >   to any testing.
> > * made sure that Selinux was in permissive mode.
> > * Made sure to have audit activated by passing "audit=1" to the kernel
> > * After noticing that some audit messages where getting lost I upped the
> >   backlog limit to 256
> > * Prior to executing the test, I also placed a breakpoint inside
> >   selinux_uring_cmd to make sure that it was executed.
> > * This is the output of the audit when I executed the test:
> >
> >   [  136.615924] audit: type=1400 audit(1662043624.701:94): avc:  denied  { create } for  pid=263 comm="io_uring_passth" anonclass=[io_uring] scontext=system_u:system_r:kernel_t tcontext=system_u:object_r:kernel_t tclass=anon_inode permissive=1
> >   [  136.621036] audit: type=1300 audit(1662043624.701:94): arch=c000003e syscall=425 success=yes exit=3 a0=40 a1=7ffca29835a0 a2=7ffca29835a0 a3=561529be2300 items=0 ppid=252 pid=263 auid=1001 uid=1001 gid=1002 euid=1001 suid=1001 fsuid=1001 egid=1002 sgid=1002 fsgid=1002 tty=pts1 ses=3 comm="io_uring_passth" exe="/mnt/src/liburing/test/io_uring_passthrough.t" subj=system_u:system_r:kernel_t key=(null)
> >   [  136.624812] audit: type=1327 audit(1662043624.701:94): proctitle=2F6D6E742F7372632F6C69627572696E672F746573742F696F5F7572696E675F706173737468726F7567682E74002F6465762F6E67306E31
> >   [  136.626074] audit: type=1400 audit(1662043624.702:95): avc:  denied  { map } for  pid=263 comm="io_uring_passth" path="anon_inode:[io_uring]" dev="anon_inodefs" ino=11715 scontext=system_u:system_r:kernel_t tcontext=system_u:object_r:kernel_t tclass=anon_inode permissive=1
> >   [  136.628012] audit: type=1400 audit(1662043624.702:95): avc:  denied  { read write } for  pid=263 comm="io_uring_passth" path="anon_inode:[io_uring]" dev="anon_inodefs" ino=11715 scontext=system_u:system_r:kernel_t tcontext=system_u:object_r:kernel_t tclass=anon_inode permissive=1
> >   [  136.629873] audit: type=1300 audit(1662043624.702:95): arch=c000003e syscall=9 success=yes exit=140179765297152 a0=0 a1=1380 a2=3 a3=8001 items=0 ppid=252 pid=263 auid=1001 uid=1001 gid=1002 euid=1001 suid=1001 fsuid=1001 egid=1002 sgid=1002 fsgid=1002 tty=pts1 ses=3 comm="io_uring_passth" exe="/mnt/src/liburing/test/io_uring_passthrough.t" subj=system_u:system_r:kernel_t key=(null)
> >   [  136.632415] audit: type=1327 audit(1662043624.702:95): proctitle=2F6D6E742F7372632F6C69627572696E672F746573742F696F5F7572696E675F706173737468726F7567682E74002F6465762F6E67306E31
> >   [  136.633652] audit: type=1400 audit(1662043624.705:96): avc:  denied  { cmd } for  pid=263 comm="io_uring_passth" path="/dev/ng0n1" dev="devtmpfs" ino=120 scontext=system_u:system_r:kernel_t tcontext=system_u:object_r:device_t tclass=io_uring permissive=1
> >   [  136.635384] audit: type=1336 audit(1662043624.705:96): uring_op=46 items=0 ppid=252 pid=263 uid=1001 gid=1002 euid=1001 suid=1001 fsuid=1001 egid=1002 sgid=1002 fsgid=1002 subj=system_u:system_r:kernel_t key=(null)
> >   [  136.636863] audit: type=1336 audit(1662043624.705:96): uring_op=46 items=0 ppid=252 pid=263 uid=1001 gid=1002 euid=1001 suid=1001 fsuid=1001 egid=1002 sgid=1002 fsgid=1002 subj=system_u:system_r:kernel_t key=(null)
> >
> > * From the output on time 136.633652 I see that the access should have
> >   been denied had selinux been enforcing.
> > * I also saw that the breakpoint hit.
> >
> > *** Without the patch:
> > * I ran the io_uring_passthrough.c test on a char device with an
> >   unpriviledged user.
> > * I took care of changing the permissions of /dev/ng0n1 to 666 prior
> >   to any testing.
> > * made sure that Selinux was in permissive mode.
> > * Made sure to have audit activated by passing "audit=1" to the kernel
> > * After noticing that some audit messages where getting lost I upped the
> >   backlog limit to 256
> > * There were no audit messages when I executed the test.
> >
> > As with my smack tests I would really appreciate feecback on the
> > approach I took to testing and it's validity.
> 
> Hi Joel,
> 
> Thanks for the additional testing and verification!  Work like this is
> always welcome, regardless if the patch has already been merged
> upstream.
np

> 
> As far as you test approach is concerned, I think you are on the right
> track, I might suggest resolving the other SELinux/AVC denials you are
> seeing with your test application to help reduce the noise in the
> logs.  Are you familiar with the selinux-testsuite (link below)?
> 
> * https://protect2.fireeye.com/v1/url?k=6f356c96-0ebe79ac-6f34e7d9-74fe4860008a-01002a6e4c92bb3e&q=1&e=46f33488-9311-49fa-9747-da210f2d147d&u=https%3A%2F%2Fgithub.com%2FSELinuxProject%2Fselinux-testsuite
Thx. Could not figure out how to remove the AVC from a quick look at the
page, but I'll probably figures something out :).

ATM, I'm doing a performance test on the io_uring_passtrhough
path to see how much, if any, perf we loose.

Thx again

Best

Joel

> 
> -- 
> paul-moore.com

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 659 bytes --]