Re: [PATCH v33 27/29] Audit: Add record for multiple object security contexts

[Casey Schaufler <casey@schaufler-ca.com>]

On 3/15/2022 4:47 PM, Paul Moore wrote:
> On Thu, Mar 10, 2022 at 7:01 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>> Create a new audit record AUDIT_MAC_OBJ_CONTEXTS.
>> An example of the MAC_OBJ_CONTEXTS (1421) record is:
>>
>>      type=MAC_OBJ_CONTEXTS[1421]
>>      msg=audit(1601152467.009:1050):
>>      obj_selinux=unconfined_u:object_r:user_home_t:s0
>>
>> When an audit event includes a AUDIT_MAC_OBJ_CONTEXTS record
>> the "obj=" field in other records in the event will be "obj=?".
>> An AUDIT_MAC_OBJ_CONTEXTS record is supplied when the system has
>> multiple security modules that may make access decisions based
>> on an object security context.
>>
>> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
>> ---
>>   include/linux/audit.h      |  5 +++
>>   include/uapi/linux/audit.h |  1 +
>>   kernel/audit.c             | 47 +++++++++++++++++++++++
>>   kernel/auditsc.c           | 79 ++++++++++++--------------------------
>>   4 files changed, 77 insertions(+), 55 deletions(-)
> ...
>
>> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
>> index af0aaccfaf57..d25d76b29e3c 100644
>> --- a/include/uapi/linux/audit.h
>> +++ b/include/uapi/linux/audit.h
>> @@ -144,6 +144,7 @@
>>   #define AUDIT_MAC_CALIPSO_ADD  1418    /* NetLabel: add CALIPSO DOI entry */
>>   #define AUDIT_MAC_CALIPSO_DEL  1419    /* NetLabel: del CALIPSO DOI entry */
>>   #define AUDIT_MAC_TASK_CONTEXTS        1420    /* Multiple LSM task contexts */
>> +#define AUDIT_MAC_OBJ_CONTEXTS 1421    /* Multiple LSM objext contexts */
>>
>>   #define AUDIT_FIRST_KERN_ANOM_MSG   1700
>>   #define AUDIT_LAST_KERN_ANOM_MSG    1799
>> diff --git a/kernel/audit.c b/kernel/audit.c
>> index ad825af203cf..ac92e7fc5aa6 100644
>> --- a/kernel/audit.c
>> +++ b/kernel/audit.c
>> @@ -2202,6 +2202,53 @@ static void audit_buffer_aux_end(struct audit_buffer *ab)
>>          ab->skb = skb_peek(&ab->skb_list);
>>   }
>>
>> +void audit_log_object_context(struct audit_buffer *ab, struct lsmblob *blob)
>> +{
>> +       int i;
>> +       int error;
>> +       struct lsmcontext context;
>> +
>> +       if (!lsm_multiple_contexts()) {
>> +               error = security_secid_to_secctx(blob, &context, LSMBLOB_FIRST);
>> +               if (error) {
>> +                       if (error != -EINVAL)
>> +                               goto error_path;
>> +                       return;
>> +               }
>> +               audit_log_format(ab, " obj=%s", context.context);
>> +               security_release_secctx(&context);
>> +       } else {
>> +               audit_log_format(ab, " obj=?");
>> +               error = audit_buffer_aux_new(ab, AUDIT_MAC_OBJ_CONTEXTS);
>> +               if (error)
>> +                       goto error_path;
>> +
>> +               for (i = 0; i < LSMBLOB_ENTRIES; i++) {
>> +                       if (blob->secid[i] == 0)
>> +                               continue;
>> +                       error = security_secid_to_secctx(blob, &context, i);
>> +                       if (error) {
>> +                               if (error != -EINVAL)
>> +                                       audit_panic("error in audit_log_object_context");
>> +                               audit_log_format(ab, "%sobj_%s=?",
>> +                                                i ? " " : "",
>> +                                                lsm_slot_to_name(i));
>> +                       } else {
>> +                               audit_log_format(ab, "%sobj_%s=%s",
>> +                                                i ? " " : "",
>> +                                                lsm_slot_to_name(i),
>> +                                                context.context);
>> +                               security_release_secctx(&context);
>> +                       }
>> +               }
>> +
>> +               audit_buffer_aux_end(ab);
>> +       }
>> +       return;
>> +
>> +error_path:
>> +       audit_panic("error in audit_log_object_context");
>> +}
> The comment from patch 26/29 regarding the audit_panic() placement
> also applies to audit_log_object_context().
>
>> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
>> index 7848e7351cf9..923e4e3a5697 100644
>> --- a/kernel/auditsc.c
>> +++ b/kernel/auditsc.c
>> @@ -1114,36 +1114,25 @@ static inline void audit_free_context(struct audit_context *context)
>>          kfree(context);
>>   }
>>
>> -static int audit_log_pid_context(struct audit_context *context, pid_t pid,
>> -                                kuid_t auid, kuid_t uid,
>> -                                unsigned int sessionid,
>> -                                struct lsmblob *blob, char *comm)
>> +static void audit_log_pid_context(struct audit_context *context, pid_t pid,
>> +                                 kuid_t auid, kuid_t uid,
>> +                                 unsigned int sessionid,
>> +                                 struct lsmblob *blob, char *comm)
>>   {
>>          struct audit_buffer *ab;
>> -       struct lsmcontext lsmctx;
>> -       int rc = 0;
>>
>>          ab = audit_log_start(context, GFP_KERNEL, AUDIT_OBJ_PID);
>>          if (!ab)
>> -               return rc;
>> +               return;
>>
>>          audit_log_format(ab, "opid=%d oauid=%d ouid=%d oses=%d", pid,
>>                           from_kuid(&init_user_ns, auid),
>>                           from_kuid(&init_user_ns, uid), sessionid);
>> -       if (lsmblob_is_set(blob)) {
>> -               if (security_secid_to_secctx(blob, &lsmctx, LSMBLOB_FIRST)) {
>> -                       audit_log_format(ab, " obj=(none)");
>> -                       rc = 1;
>> -               } else {
>> -                       audit_log_format(ab, " obj=%s", lsmctx.context);
>> -                       security_release_secctx(&lsmctx);
>> -               }
>> -       }
>> +       if (lsmblob_is_set(blob))
>> +               audit_log_object_context(ab, blob);
>>          audit_log_format(ab, " ocomm=");
>>          audit_log_untrustedstring(ab, comm);
>>          audit_log_end(ab);
>> -
>> -       return rc;
>>   }
>>
>>   static void audit_log_execve_info(struct audit_context *context,
>> @@ -1373,18 +1362,10 @@ static void show_special(struct audit_context *context, int *call_panic)
>>                                   from_kgid(&init_user_ns, context->ipc.gid),
>>                                   context->ipc.mode);
>>                  if (osid) {
>> -                       struct lsmcontext lsmcxt;
>>                          struct lsmblob blob;
>>
>>                          lsmblob_init(&blob, osid);
>> -                       if (security_secid_to_secctx(&blob, &lsmcxt,
>> -                                                    LSMBLOB_FIRST)) {
>> -                               audit_log_format(ab, " osid=%u", osid);
>> -                               *call_panic = 1;
>> -                       } else {
>> -                               audit_log_format(ab, " obj=%s", lsmcxt.context);
>> -                               security_release_secctx(&lsmcxt);
>> -                       }
>> +                       audit_log_object_context(ab, &blob);
> While we lose the "osid=X" in case of failure, the secid/SID is a
> private kernel value meaning it was always of questionable value.

I could come up with a change to audit_log_object_context() that
would put out an osid= in the single security module case. I would
prefer not to if that would be acceptable.

>
>
> --
> paul-moore.com