audit: restore AUDIT_LOGINUID unset ABI

A regression was caused by commit 780a7654cee8:
	 audit: Make testing for a valid loginuid explicit.
(which in turn attempted to fix a regression caused by e1760bd)

When audit_krule_to_data() fills in the rules to get a listing, there was a
missing clause to convert back from AUDIT_LOGINUID_SET to AUDIT_LOGINUID.

This broke userspace by not returning the same information that was sent and
expected.

The rule:
	auditctl -a exit,never -F auid=-1
gives:
	auditctl -l
		LIST_RULES: exit,never f24=0 syscall=all
when it should give:
		LIST_RULES: exit,never auid=-1 (0xffffffff) syscall=all

Tag it so that it is reported the same way it was set.  Create a new
private flags audit_krule field (pflags) to store it that won't interact with
the public one from the API.

Cc: stable@vger.kernel.org # v3.10-rc1+
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>

2 files changed, 14 insertions, 0 deletions

diff --git a/include/linux/audit.h b/include/linux/audit.h
index 36dffeccebdb..93331929d643 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -47,6 +47,7 @@ struct sk_buff;
 
 struct audit_krule {
         int                     vers_ops;
+        u32                     pflags;
         u32                     flags;
         u32                     listnr;
         u32                     action;
@@ -64,6 +65,9 @@ struct audit_krule {
         u64                     prio;
 };
 
+/* Flag to indicate legacy AUDIT_LOGINUID unset usage */
+#define AUDIT_LOGINUID_LEGACY           0x1
+
 struct audit_field {
         u32                             type;
         union {
diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index c0d148bd7a5c..103586e239a2 100644
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -442,6 +442,7 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
                 if ((f->type == AUDIT_LOGINUID) && (f->val == AUDIT_UID_UNSET)) {
                         f->type = AUDIT_LOGINUID_SET;
                         f->val = 0;
+                        entry->rule.pflags |= AUDIT_LOGINUID_LEGACY;
                 }
 
                 err = audit_field_valid(entry, f);
@@ -617,6 +618,13 @@ static struct audit_rule_data *audit_krule_to_data(struct audit_krule *krule)
                         data->buflen += data->values[i] =
                                 audit_pack_string(&bufp, krule->filterkey);
                         break;
+                case AUDIT_LOGINUID_SET:
+                        if (krule->pflags & AUDIT_LOGINUID_LEGACY && !f->val) {
+                                data->fields[i] = AUDIT_LOGINUID;
+                                data->values[i] = AUDIT_UID_UNSET;
+                                break;
+                        }
+                        /* fallthrough if set */
                 default:
                         data->values[i] = f->val;
                 }
@@ -633,6 +641,7 @@ static int audit_compare_rule(struct audit_krule *a, struct audit_krule *b)
         int i;
 
         if (a->flags != b->flags ||
+            a->pflags != b->pflags ||
             a->listnr != b->listnr ||
             a->action != b->action ||
             a->field_count != b->field_count)
@@ -751,6 +760,7 @@ struct audit_entry *audit_dupe_rule(struct audit_krule *old)
         new = &entry->rule;
         new->vers_ops = old->vers_ops;
         new->flags = old->flags;
+        new->pflags = old->pflags;
         new->listnr = old->listnr;
         new->action = old->action;
         for (i = 0; i < AUDIT_BITMASK_SIZE; i++)