SELinux: do not allocate stack space for AVC data unless needed

Instead of declaring the entire selinux_audit_data on the stack when we
start an operation on declare it on the stack if we are going to use it.
We know it's usefulness at the end of the security decision and can declare
it there.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 12 deletions

diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index b5545a84448..36c42bb52d8 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -436,9 +436,9 @@ static void avc_audit_pre_callback(struct audit_buffer *ab, void *a)
 {
 	struct common_audit_data *ad = a;
 	audit_log_format(ab, "avc:  %s ",
-			 ad->selinux_audit_data->denied ? "denied" : "granted");
-	avc_dump_av(ab, ad->selinux_audit_data->tclass,
-			ad->selinux_audit_data->audited);
+			 ad->selinux_audit_data->slad->denied ? "denied" : "granted");
+	avc_dump_av(ab, ad->selinux_audit_data->slad->tclass,
+			ad->selinux_audit_data->slad->audited);
 	audit_log_format(ab, " for ");
 }
 
@@ -452,9 +452,9 @@ static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
 {
 	struct common_audit_data *ad = a;
 	audit_log_format(ab, " ");
-	avc_dump_query(ab, ad->selinux_audit_data->ssid,
-			   ad->selinux_audit_data->tsid,
-			   ad->selinux_audit_data->tclass);
+	avc_dump_query(ab, ad->selinux_audit_data->slad->ssid,
+			   ad->selinux_audit_data->slad->tsid,
+			   ad->selinux_audit_data->slad->tclass);
 }
 
 /* This is the slow part of avc audit with big stack footprint */
@@ -465,6 +465,7 @@ static noinline int slow_avc_audit(u32 ssid, u32 tsid, u16 tclass,
 {
 	struct common_audit_data stack_data;
 	struct selinux_audit_data sad = {0,};
+	struct selinux_late_audit_data slad;
 
 	if (!a) {
 		a = &stack_data;
@@ -483,12 +484,14 @@ static noinline int slow_avc_audit(u32 ssid, u32 tsid, u16 tclass,
 	    (flags & MAY_NOT_BLOCK))
 		return -ECHILD;
 
-	a->selinux_audit_data->tclass = tclass;
-	a->selinux_audit_data->requested = requested;
-	a->selinux_audit_data->ssid = ssid;
-	a->selinux_audit_data->tsid = tsid;
-	a->selinux_audit_data->audited = audited;
-	a->selinux_audit_data->denied = denied;
+	slad.tclass = tclass;
+	slad.requested = requested;
+	slad.ssid = ssid;
+	slad.tsid = tsid;
+	slad.audited = audited;
+	slad.denied = denied;
+
+	a->selinux_audit_data->slad = &slad;
 	a->lsm_pre_audit = avc_audit_pre_callback;
 	a->lsm_post_audit = avc_audit_post_callback;
 	common_lsm_audit(a);