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Subject: Re: [PATCH v4 8/8] module: replace the existing LSM hook in
 init_module
From:   Mimi Zohar <zohar@linux.vnet.ibm.com>
To:     Paul Moore <paul@paul-moore.com>, Kees Cook <keescook@chromium.org>
Cc:     linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, David Howells <dhowells@redhat.com>,
        "Luis R . Rodriguez" <mcgrof@kernel.org>,
        Eric Biederman <ebiederm@xmission.com>,
        kexec@lists.infradead.org, Andres Rodriguez <andresx7@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Jeff Vander Stoep <jeffv@google.com>,
        Casey Schaufler <casey@schaufler-ca.com>
Date:   Tue, 29 May 2018 19:25:02 -0400
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         <CAHC9VhQL+CsqKL83fSZhjEZVSjKKfmLULvehXZ8SZhtK5xzLMQ@mail.gmail.com>
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Hi Kees,

Missing from this patch are the loadpin changes.  Before including
them in the next version of this patch, do you prefer separating the
init_module from the finit_module support in loadpin_read_file() or
keeping it as one function, like Paul for SELinux?

Mimi

On Tue, 2018-05-29 at 18:39 -0400, Paul Moore wrote:
> On Tue, May 29, 2018 at 2:02 PM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
> > Both the init_module and finit_module syscalls call either directly
> > or indirectly the security_kernel_read_file LSM hook.  This patch
> > replaces the direct call in init_module with a call to the new
> > security_kernel_load_data hook and makes the corresponding changes in
> > SELinux and IMA.
> >
> > Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
> > Cc: Jeff Vander Stoep <jeffv@google.com>
> > Cc: Paul Moore <paul@paul-moore.com>
> > Cc: Casey Schaufler <casey@schaufler-ca.com>
> > ---
> >  kernel/module.c                   |  2 +-
> >  security/integrity/ima/ima_main.c | 24 ++++++++++--------------
> >  security/selinux/hooks.c          | 26 ++++++++++++++++++++------
> >  3 files changed, 31 insertions(+), 21 deletions(-)
> >
> > diff --git a/kernel/module.c b/kernel/module.c
> > index ce8066b88178..b97c642b5b4d 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -2879,7 +2879,7 @@ static int copy_module_from_user(const void __user *umod, unsigned long len,
> >         if (info->len < sizeof(*(info->hdr)))
> >                 return -ENOEXEC;
> >
> > -       err = security_kernel_read_file(NULL, READING_MODULE);
> > +       err = security_kernel_load_data(LOADING_MODULE);
> >         if (err)
> >                 return err;
> >
> > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> > index 3dae605a1604..0ff1d8152f6e 100644
> > --- a/security/integrity/ima/ima_main.c
> > +++ b/security/integrity/ima/ima_main.c
> > @@ -441,17 +441,6 @@ static int read_idmap[READING_MAX_ID] = {
> >   */
> >  int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
> >  {
> > -       bool sig_enforce = is_module_sig_enforced();
> > -
> > -       if (!file && read_id == READING_MODULE) {
> > -               if (!sig_enforce && (ima_appraise & IMA_APPRAISE_MODULES) &&
> > -                   (ima_appraise & IMA_APPRAISE_ENFORCE)) {
> > -                       pr_err("impossible to appraise a module without a file descriptor. sig_enforce kernel parameter might help\n");
> > -                       return -EACCES; /* INTEGRITY_UNKNOWN */
> > -               }
> > -               return 0;       /* We rely on module signature checking */
> > -       }
> > -
> >         if (read_id == READING_FIRMWARE_PREALLOC_BUFFER) {
> >                 if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
> >                     (ima_appraise & IMA_APPRAISE_ENFORCE)) {
> > @@ -490,9 +479,6 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
> >                 return 0;
> >         }
> >
> > -       if (!file && read_id == READING_MODULE) /* MODULE_SIG_FORCE enabled */
> > -               return 0;
> > -
> >         /* permit signed certs */
> >         if (!file && read_id == READING_X509_CERTIFICATE)
> >                 return 0;
> > @@ -521,6 +507,8 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
> >   */
> >  int ima_load_data(enum kernel_load_data_id id)
> >  {
> > +       bool sig_enforce;
> > +
> >         if ((ima_appraise & IMA_APPRAISE_ENFORCE) != IMA_APPRAISE_ENFORCE)
> >                 return 0;
> >
> > @@ -536,6 +524,14 @@ int ima_load_data(enum kernel_load_data_id id)
> >                         pr_err("Prevent firmware sysfs fallback loading.\n");
> >                         return -EACCES; /* INTEGRITY_UNKNOWN */
> >                 }
> > +               break;
> > +       case LOADING_MODULE:
> > +               sig_enforce = is_module_sig_enforced();
> > +
> > +               if (!sig_enforce && (ima_appraise & IMA_APPRAISE_MODULES)) {
> > +                       pr_err("impossible to appraise a module without a file descriptor. sig_enforce kernel parameter might help\n");
> > +                       return -EACCES; /* INTEGRITY_UNKNOWN */
> > +               }
> >         default:
> >                 break;
> >         }
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index 02ebd1585eaf..e02186470fc5 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -4018,12 +4018,6 @@ static int selinux_kernel_module_from_file(struct file *file)
> >         u32 sid = current_sid();
> >         int rc;
> >
> > -       /* init_module */
> > -       if (file == NULL)
> > -               return avc_has_perm(&selinux_state,
> > -                                   sid, sid, SECCLASS_SYSTEM,
> > -                                       SYSTEM__MODULE_LOAD, NULL);
> > -
> >         /* finit_module */
> >
> >         ad.type = LSM_AUDIT_DATA_FILE;
> > @@ -4043,6 +4037,25 @@ static int selinux_kernel_module_from_file(struct file *file)
> >                                 SYSTEM__MODULE_LOAD, &ad);
> >  }
> >
> > +static int selinux_kernel_load_data(enum kernel_load_data_id id)
> > +{
> > +       u32 sid;
> > +       int rc = 0;
> > +
> > +       switch (id) {
> > +       case LOADING_MODULE:
> > +               sid = current_sid();
> > +
> > +               /* init_module */
> > +               return avc_has_perm(&selinux_state, sid, sid, SECCLASS_SYSTEM,
> > +                                   SYSTEM__MODULE_LOAD, NULL);
> > +       default:
> > +               break;
> > +       }
> > +
> > +       return rc;
> > +}
> 
> I'm not a fan of the duplication here.  If we must have a new LSM hook
> for this, can we at least have it call
> selinux_kernel_module_from_file() so we have all the kernel module
> loading logic/controls in one function?  Yes, I understand there are
> differences between init_module() and finit_module() but I like
> handling them both in one function as we do today.
> 
> >  static int selinux_kernel_read_file(struct file *file,
> >                                     enum kernel_read_file_id id)
> >  {
> > @@ -6950,6 +6963,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
> >         LSM_HOOK_INIT(kernel_act_as, selinux_kernel_act_as),
> >         LSM_HOOK_INIT(kernel_create_files_as, selinux_kernel_create_files_as),
> >         LSM_HOOK_INIT(kernel_module_request, selinux_kernel_module_request),
> > +       LSM_HOOK_INIT(kernel_load_data, selinux_kernel_load_data),
> >         LSM_HOOK_INIT(kernel_read_file, selinux_kernel_read_file),
> >         LSM_HOOK_INIT(task_setpgid, selinux_task_setpgid),
> >         LSM_HOOK_INIT(task_getpgid, selinux_task_getpgid),
> > --
> > 2.7.5
> >
>