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From:   Paul Moore <paul@paul-moore.com>
Date:   Fri, 27 Jan 2023 19:06:28 -0500
Message-ID: <CAHC9VhSN+XSYGh0TBsCPftNvVNBN1JHugrrsp3gbF-in5S1PoA@mail.gmail.com>
Subject: Re: [PATCH v1 2/2] io_uring,audit: do not log IORING_OP_*GETXATTR
To:     Richard Guy Briggs <rgb@redhat.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>
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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.

-- 
paul-moore.com