linux-kernel - [PATCH v2] selinux: fix double free of cond

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Date:   Wed,  2 Feb 2022 12:25:11 +0100
From:   vbendel@...hat.com
To:     paul@...l-moore.com, stephen.smalley.work@...il.com,
        eparis@...isplace.org
Cc:     omosnace@...hat.com, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org, Vratislav Bendel <vbendel@...hat.com>
Subject: [PATCH v2] selinux: fix double free of cond_list on error paths

From: Vratislav Bendel <vbendel@...hat.com>

On error path from cond_read_list() and duplicate_policydb_cond_list()
the cond_list_destroy() gets called a second time in caller functions,
resulting in NULL pointer deref.
Fix this by resetting the cond_list_len to 0 in cond_list_destroy(),
making subsequent calls a noop.

Also consistently reset the cond_list pointer to NULL after freeing.

Signed-off-by: Vratislav Bendel <vbendel@...hat.com>
---
 security/selinux/ss/conditional.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/security/selinux/ss/conditional.c b/security/selinux/ss/conditional.c
index 2ec6e5cd25d9..feb206f3acb4 100644
--- a/security/selinux/ss/conditional.c
+++ b/security/selinux/ss/conditional.c
@@ -152,6 +152,8 @@ static void cond_list_destroy(struct policydb *p)
 	for (i = 0; i < p->cond_list_len; i++)
 		cond_node_destroy(&p->cond_list[i]);
 	kfree(p->cond_list);
+	p->cond_list = NULL;
+	p->cond_list_len = 0;
 }
 
 void cond_policydb_destroy(struct policydb *p)
@@ -441,7 +443,6 @@ int cond_read_list(struct policydb *p, void *fp)
 	return 0;
 err:
 	cond_list_destroy(p);
-	p->cond_list = NULL;
 	return rc;
 }
 
-- 
2.26.3