[PATCH v2 1/1] selinux: fix another double free

From: trix@redhat.com
To: paul@paul-moore.com, stephen.smalley.work@gmail.com,
	eparis@parisplace.org, omosnace@redhat.com,
	weiyongjun1@huawei.com
Cc: selinux@vger.kernel.org, linux-kernel@vger.kernel.org,
	Tom Rix <trix@redhat.com>
Subject: [PATCH v2 1/1] selinux: fix another double free
Date: Thu, 11 Jun 2020 13:47:46 -0700	[thread overview]
Message-ID: <20200611204746.6370-2-trix@redhat.com> (raw)
In-Reply-To: <20200611204746.6370-1-trix@redhat.com>

From: Tom Rix <trix@redhat.com>

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.

Fixes a problem was introduced by commit

  selinux: convert cond_list to array

Signed-off-by: Tom Rix <trix@redhat.com>
---
 security/selinux/ss/conditional.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/security/selinux/ss/conditional.c b/security/selinux/ss/conditional.c
index da94a1b4bfda..d0d6668709f0 100644
--- a/security/selinux/ss/conditional.c
+++ b/security/selinux/ss/conditional.c
@@ -392,26 +392,21 @@ 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;
+			return rc;
 		}
 	}
 
 	rc = cond_read_av_list(p, fp, &node->true_list, NULL);
 	if (rc)
-		goto err;
+		return rc;
 	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;
 }
 
-- 
2.18.1

