Date:   Fri, 27 Jan 2023 19:19:31 -0500
From:   Richard Guy Briggs <rgb@redhat.com>
To:     Paul Moore <paul@paul-moore.com>
Cc:     Linux-Audit Mailing List <linux-audit@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, io-uring@vger.kernel.org,
        Eric Paris <eparis@parisplace.org>,
        Steve Grubb <sgrubb@redhat.com>, Stefan Roesch <shr@fb.com>,
        Christian Brauner <brauner@kernel.org>,
        Jens Axboe <axboe@kernel.dk>,
        Pavel Begunkov <asml.silence@gmail.com>
Subject: Re: [PATCH v1 2/2] io_uring,audit: do not log IORING_OP_*GETXATTR
Message-ID: <Y9RqEz/qQYmp5jD+@madcap2.tricolour.ca>
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On 2023-01-27 19:06, Paul Moore wrote:
> On Fri, Jan 27, 2023 at 6:01 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> > On 2023-01-27 17:43, Paul Moore wrote:
> > > On Fri, Jan 27, 2023 at 12:24 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> > > > Getting XATTRs is not particularly interesting security-wise.
> > > >
> > > > Suggested-by: Steve Grubb <sgrubb@redhat.com>
> > > > Fixes: a56834e0fafe ("io_uring: add fgetxattr and getxattr support")
> > > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > > > ---
> > > >  io_uring/opdef.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > >
> > > Depending on your security policy, fetching file data, including
> > > xattrs, can be interesting from a security perspective.  As an
> > > example, look at the SELinux file/getattr permission.
> > >
> > > https://github.com/SELinuxProject/selinux-notebook/blob/main/src/object_classes_permissions.md#common-file-permissions
> >
> > The intent here is to lessen the impact of audit operations.  Read and
> > Write were explicitly removed from io_uring auditing due to performance
> > concerns coupled with the denial of service implications from sheer
> > volume of records making other messages harder to locate.  Those
> > operations are still possible for syscall auditing but they are strongly
> > discouraged for normal use.
> 
> We need to balance security needs and performance needs.  You are
> correct that general read() and write() operations are not audited,
> and generally not checked from a LSM perspective as the auditing and
> access control happens at open() time instead (access to fds is
> revalidated when they are passed).  However, in the case of getxattr
> and fgetxattr, these are not normal file read operations, and do not
> go through the same code path in the kernel; there is a reason why we
> have xattr_permission() and security_inode_getxattr().
> 
> We need to continue to audit IORING_OP_FGETXATTR and IORING_OP_GETXATTR.

Fair enough.  This would be similar reasoning to send/recv vs
sendmsg/recvmsg.  I'll drop this patch.  Thanks for the reasoning and
feedback.

> paul-moore.com

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635