References: bnc#860163 XSA-84

flask: restrict allocations done by hypercall interface

Other than in 4.2 and newer, we're not having an overflow issue here,
but uncontrolled exposure of the operations opens the host to be driven
out of memory by an arbitrary guest. Since all operations other than
FLASK_LOAD simply deal with ASCII strings, limiting the allocations
(and incoming buffer sizes) to a page worth of memory seems like the
best thing we can do.

Consequently, in order to not expose the larger allocation to arbitrary
guests, the permission check for FLASK_LOAD needs to be pulled ahead of
the allocation (and it's perhaps worth noting that - afaict - it was
pointlessly done with the sel_sem spin lock held).

Note that this breaks FLASK_AVC_CACHESTATS on systems with sufficiently
many CPUs (as requiring a buffer bigger than PAGE_SIZE there). No
attempt is made to address this here, as it would needlessly complicate
this fix with rather little gain.

This is XSA-84.

Reported-by: Matthew Daley <mattd@bugfuzz.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>

The index of boolean variables in FLASK_{GET,SET}BOOL was not always
checked against the bounds of the array.

Reported-by: John McDermott <john.mcdermott@nrl.navy.mil>
Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>

--- a/xen/xsm/flask/flask_op.c
+++ b/xen/xsm/flask/flask_op.c
@@ -573,7 +573,7 @@ static int flask_security_setavc_thresho
 static int flask_security_set_bool(char *buf, uint32_t count)
 {
     int length = -EFAULT;
-    int i, new_value;
+    unsigned int i, new_value;
 
     spin_lock(&sel_sem);
 
@@ -585,6 +585,9 @@ static int flask_security_set_bool(char 
     if ( sscanf(buf, "%d %d", &i, &new_value) != 2 )
         goto out;
 
+    if ( i >= bool_num )
+        goto out;
+
     if ( new_value )
     {
         new_value = 1;
@@ -734,10 +737,6 @@ static int flask_security_load(char *buf
 
     spin_lock(&sel_sem);
 
-    length = domain_has_security(current->domain, SECURITY__LOAD_POLICY);
-    if ( length )
-        goto out;
-
     length = security_load_policy(buf, count);
     if ( length )
         goto out;
@@ -853,7 +852,15 @@ long do_flask_op(XEN_GUEST_HANDLE(xsm_op
     if ( op->cmd > FLASK_LAST)
         return -EINVAL;
 
-    if ( op->size > MAX_POLICY_SIZE )
+    if ( op->cmd == FLASK_LOAD )
+    {
+        rc = domain_has_security(current->domain, SECURITY__LOAD_POLICY);
+        if ( rc )
+            return rc;
+        if ( op->size > MAX_POLICY_SIZE )
+            return -EINVAL;
+    }
+    else if ( op->size >= PAGE_SIZE )
         return -EINVAL;
 
     if ( (op->buf == NULL && op->size != 0) || 
--- a/xen/xsm/flask/ss/services.c
+++ b/xen/xsm/flask/ss/services.c
@@ -1991,7 +1991,7 @@ int security_get_bool_value(int bool)
     POLICY_RDLOCK;
 
     len = policydb.p_bools.nprim;
-    if ( bool >= len )
+    if ( bool >= len || bool < 0 )
     {
         rc = -EFAULT;
         goto out;