[PATCH 1/5] audit: allow interfield comparison in audit rules

Eric Paris
2012-01-04T20:47:09Z

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>
---
include/linux/audit.h | 4 ++++
kernel/auditfilter.c | 5 ++++-
kernel/auditsc.c | 30 +++++++++++++++++++++++++++++-
3 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/include/linux/audit.h b/include/linux/audit.h
index c1048b6..7bf31e2 100644
--- 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
--- 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 37ad085..efb1763 100644
--- 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;
}
--
1.7.1