linux-kernel - [PATCH v23 18/23] LSM: Verify LSM display sanity in binder

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20201120201507.11993-19-casey@schaufler-ca.com>
Date:   Fri, 20 Nov 2020 12:15:02 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     casey.schaufler@...el.com, jmorris@...ei.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org
Cc:     casey@...aufler-ca.com, linux-audit@...hat.com,
        keescook@...omium.org, john.johansen@...onical.com,
        penguin-kernel@...ove.sakura.ne.jp, paul@...l-moore.com,
        sds@...ho.nsa.gov, linux-kernel@...r.kernel.org
Subject: [PATCH v23 18/23] LSM: Verify LSM display sanity in binder

Verify that the tasks on the ends of a binder transaction
use the same "display" security module. This prevents confusion
of security "contexts".

Reviewed-by: Kees Cook <keescook@...omium.org>
Reviewed-by: John Johansen <john.johansen@...onical.com>
Acked-by: Stephen Smalley <sds@...ho.nsa.gov>
Acked-by: Paul Moore <paul@...l-moore.com>
Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
---
 security/security.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/security/security.c b/security/security.c
index 31c983a252b9..8803347424d4 100644
--- a/security/security.c
+++ b/security/security.c
@@ -791,9 +791,38 @@ int security_binder_set_context_mgr(struct task_struct *mgr)
 	return call_int_hook(binder_set_context_mgr, 0, mgr);
 }
 
+/**
+ * security_binder_transaction - Binder driver transaction check
+ * @from: source of the transaction
+ * @to: destination of the transaction
+ *
+ * Verify that the tasks have the same LSM "display", then
+ * call the security module hooks.
+ *
+ * Returns -EINVAL if the displays don't match, or the
+ * result of the security module checks.
+ */
 int security_binder_transaction(struct task_struct *from,
 				struct task_struct *to)
 {
+	int from_ilsm = lsm_task_ilsm(from);
+	int to_ilsm = lsm_task_ilsm(to);
+
+	/*
+	 * If the ilsm is LSMBLOB_INVALID the first module that has
+	 * an entry is used. This will be in the 0 slot.
+	 *
+	 * This is currently only required if the server has requested
+	 * peer contexts, but it would be unwieldly to have too much of
+	 * the binder driver detail here.
+	 */
+	if (from_ilsm == LSMBLOB_INVALID)
+		from_ilsm = 0;
+	if (to_ilsm == LSMBLOB_INVALID)
+		to_ilsm = 0;
+	if (from_ilsm != to_ilsm)
+		return -EINVAL;
+
 	return call_int_hook(binder_transaction, 0, from, to);
 }
 
-- 
2.24.1