selinux: fix a double free in cond_read_node()/cond_read_list()

Clang static analysis reports this double free error

security/selinux/ss/conditional.c:139:2: warning: Attempt to free released memory [unix.Malloc]
        kfree(node->expr.nodes);
        ^~~~~~~~~~~~~~~~~~~~~~~

When cond_read_node fails, it calls cond_node_destroy which frees the
node but does not poison the entry in the node list.  So when it
returns to its caller cond_read_list, cond_read_list deletes the
partial list.  The latest entry in the list will be deleted twice.

So instead of freeing the node in cond_read_node, let list freeing in
code_read_list handle the freeing the problem node along with all of the
earlier nodes.

Because cond_read_node no longer does any error handling, the goto's
the error case are redundant.  Instead just return the error code.

Cc: stable@vger.kernel.org
Fixes: 60abd3181db2 ("selinux: convert cond_list to array")
Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Ondrej Mosnacek <omosnace@redhat.com>
[PM: subject line tweaks]
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/security/selinux/ss/conditional.c b/security/selinux/ss/conditional.c
index 939a74fd8fb470e68ef6fd9172a11fd2e42679d4..4867dfc5337ac17ee7e803918d7c20b382f6fb56 100644 (file)
--- a/security/selinux/ss/conditional.c
+++ b/security/selinux/ss/conditional.c
@@ -392,27 +392,19 @@ static int cond_read_node(struct policydb *p, struct cond_node *node, void *fp)
 
                rc = next_entry(buf, fp, sizeof(u32) * 2);
                if (rc)
-                       goto err;
+                       return rc;
 
                expr->expr_type = le32_to_cpu(buf[0]);
                expr->bool = le32_to_cpu(buf[1]);
 
-               if (!expr_node_isvalid(p, expr)) {
-                       rc = -EINVAL;
-                       goto err;
-               }
+               if (!expr_node_isvalid(p, expr))
+                       return -EINVAL;
        }
 
        rc = cond_read_av_list(p, fp, &node->true_list, NULL);
        if (rc)
-               goto err;
-       rc = cond_read_av_list(p, fp, &node->false_list, &node->true_list);
-       if (rc)
-               goto err;
-       return 0;
-err:
-       cond_node_destroy(node);
-       return rc;
+               return rc;
+       return cond_read_av_list(p, fp, &node->false_list, &node->true_list);
 }
 
 int cond_read_list(struct policydb *p, void *fp)