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audit: allow interfield comparison in audit rules

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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>
This commit is contained in:
Eric Paris 2012-01-03 14:23:08 -05:00 committed by Al Viro
parent 29ef73b7a8
commit 02d86a568c
3 changed files with 37 additions and 2 deletions
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4
include/linux/audit.h
View File

@ -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)

5
kernel/auditfilter.c
View File

@ -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;
}

30
kernel/auditsc.c
View File

@ -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;
}