linux-kernel - [PATCH v3] selinux: fix another double free

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Date:   Mon, 15 Jun 2020 13:45:48 -0700
From:   trix@...hat.com
To:     paul@...l-moore.com, stephen.smalley.work@...il.com,
        eparis@...isplace.org, omosnace@...hat.com, weiyongjun1@...wei.com
Cc:     selinux@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tom Rix <trix@...hat.com>
Subject: [PATCH v3] selinux: fix another double free

From: Tom Rix <trix@...hat.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: 60abd3181db2 ("selinux: convert cond_list to array")

Signed-off-by: Tom Rix <trix@...hat.com>
---
v3: simplify returns

 security/selinux/ss/conditional.c | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/security/selinux/ss/conditional.c b/security/selinux/ss/conditional.c
index da94a1b4bfda..450bc02f4cd2 100644
--- 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)
-- 
2.18.1