audit: allow interfield comparison in audit rules

We wish to be able to audit when a uid=500 task accesses a file which is
uid=0.  Or vice versa.  This patch introduces a new audit filter type
AUDIT_FIELD_COMPARE which takes as an 'enum' which indicates which fields
should be compared.  At this point we only define the task->uid vs
inode->uid, but other comparisons can be added.

Signed-off-by: Eric Paris <eparis@redhat.com>

diff --git a/include/linux/audit.h b/include/linux/audit.h
index 7cbd6fe..838e05f 100644 (file)
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -182,7 +182,10 @@
  * AUDIT_UNUSED_BITS is updated if need be. */
 #define AUDIT_UNUSED_BITS      0x07FFFC00
 
+/* AUDIT_FIELD_COMPARE rule list */
+#define AUDIT_COMPARE_UID_TO_OBJ_UID   1
 
+#define AUDIT_MAX_FIELD_COMPARE        AUDIT_COMPARE_UID_TO_OBJ_UID
 /* Rule fields */
                                /* These are useful when checking the
                                 * task structure at task creation time
@@ -225,6 +228,7 @@
 #define AUDIT_FILETYPE 108
 #define AUDIT_OBJ_UID  109
 #define AUDIT_OBJ_GID  110
+#define AUDIT_FIELD_COMPARE    111
 
 #define AUDIT_ARG0      200
 #define AUDIT_ARG1      (AUDIT_ARG0+1)

diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index f10605c..a6c3f1a 100644 (file)
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -526,7 +526,6 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
                                goto exit_free;
                        break;
                case AUDIT_FILTERKEY:
-                       err = -EINVAL;
                        if (entry->rule.filterkey || f->val > AUDIT_MAX_KEY_LEN)
                                goto exit_free;
                        str = audit_unpack_string(&bufp, &remain, f->val);
@@ -543,6 +542,10 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
                        if (f->val & ~S_IFMT)
                                goto exit_free;
                        break;
+               case AUDIT_FIELD_COMPARE:
+                       if (f->val > AUDIT_MAX_FIELD_COMPARE)
+                               goto exit_free;
+                       break;
                default:
                        goto exit_free;
                }

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 9161e70..8fb2c8e 100644 (file)
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -463,6 +463,32 @@ static int match_tree_refs(struct audit_context *ctx, struct audit_tree *tree)
        return 0;
 }
 
+static int audit_field_compare(struct task_struct *tsk,
+                              const struct cred *cred,
+                              struct audit_field *f,
+                              struct audit_context *ctx,
+                              struct audit_names *name)
+{
+       struct audit_names *n;
+
+       switch (f->val) {
+       case AUDIT_COMPARE_UID_TO_OBJ_UID:
+               if (name) {
+                       return audit_comparator(cred->uid, f->op, name->uid);
+               } else if (ctx) {
+                       list_for_each_entry(n, &ctx->names_list, list) {
+                               if (audit_comparator(cred->uid, f->op, n->uid))
+                                       return 1;
+                       }
+               }
+               break;
+       default:
+               WARN(1, "Missing AUDIT_COMPARE define.  Report as a bug\n");
+               return 0;
+       }
+       return 0;
+}
+
 /* Determine if any context name data matches a rule's watch data */
 /* Compare a task_struct with an audit_rule.  Return 1 on match, 0
  * otherwise.
@@ -693,8 +719,10 @@ static int audit_filter_rules(struct task_struct *tsk,
                case AUDIT_FILETYPE:
                        result = audit_match_filetype(ctx, f->val);
                        break;
+               case AUDIT_FIELD_COMPARE:
+                       result = audit_field_compare(tsk, cred, f, ctx, name);
+                       break;
                }
-
                if (!result)
                        return 0;
        }