[PATCH 2/2] audit: restore AUDIT_LOGINUID unset ABI

[Richard Guy Briggs <rgb@xxxxxxxxxx>]

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.

Cc: stable@xxxxxxxxxxxxxxx # v3.10-rc1+
Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
---
 include/linux/audit.h |    3 +++
 kernel/auditfilter.c  |   10 +++++++++-
 2 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/include/linux/audit.h b/include/linux/audit.h
index eefc39a..d905832 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -63,6 +63,9 @@ struct audit_krule {
 	u64			prio;
 };
 
+/* Flag to indicate legacy AUDIT_LOGINUID unset usage */
+#define AUDIT_LOGINUID_LEGACY		0x80000000
+
 struct audit_field {
 	u32				type;
 	union {
diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index fb4d2df..ea62c7b 100644
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -441,6 +441,7 @@ 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.flags |= AUDIT_LOGINUID_LEGACY;
 		}
 
 		if ((f->type == AUDIT_PID) || (f->type == AUDIT_PPID)) {
@@ -592,7 +593,7 @@ static struct audit_rule_data *audit_krule_to_data(struct audit_krule *krule)
 		return NULL;
 	memset(data, 0, sizeof(*data));
 
-	data->flags = krule->flags | krule->listnr;
+	data->flags = (krule->flags & ~AUDIT_LOGINUID_LEGACY) | krule->listnr;
 	data->action = krule->action;
 	data->field_count = krule->field_count;
 	bufp = data->buf;
@@ -629,6 +630,13 @@ 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->flags & 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;
 		}
-- 
1.7.1

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