linux-kernel - [QUEUED v0 04/19] stm class: Fix locking in unbinding policy path

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-Id: <1454690128-21994-5-git-send-email-alexander.shishkin@linux.intel.com>
Date:	Fri,  5 Feb 2016 18:35:13 +0200
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Greg KH <greg@...ah.com>
Cc:	Mathieu Poirier <mathieu.poirier@...aro.org>,
	Chunyan Zhang <zhang.chunyan@...aro.org>,
	laurent.fert@...el.com, yann.fouassier@...el.com,
	linux-kernel@...r.kernel.org,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: [QUEUED v0 04/19] stm class: Fix locking in unbinding policy path

Right now, if stm device removal has to unbind from a policy (that is,
an stm device that has STP policy, gets removed), it will trigger a
nested lock on the stm device's policy mutex.

This patch fixes the problem by moving the locking from the policy
unbinding to policy removal (configfs path), where it's actually needed;
the other caller of the policy unbinding function already takes the
mutex around the call.

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
---
 drivers/hwtracing/stm/policy.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/hwtracing/stm/policy.c b/drivers/hwtracing/stm/policy.c
index 11ab6d01ad..94d3abfb73 100644
--- a/drivers/hwtracing/stm/policy.c
+++ b/drivers/hwtracing/stm/policy.c
@@ -272,13 +272,17 @@ void stp_policy_unbind(struct stp_policy *policy)
 {
 	struct stm_device *stm = policy->stm;
 
+	/*
+	 * stp_policy_release() will not call here if the policy is already
+	 * unbound; other users should not either, as no link exists between
+	 * this policy and anything else in that case
+	 */
 	if (WARN_ON_ONCE(!policy->stm))
 		return;
 
-	mutex_lock(&stm->policy_mutex);
-	stm->policy = NULL;
-	mutex_unlock(&stm->policy_mutex);
+	lockdep_assert_held(&stm->policy_mutex);
 
+	stm->policy = NULL;
 	policy->stm = NULL;
 
 	stm_put_device(stm);
@@ -287,8 +291,16 @@ void stp_policy_unbind(struct stp_policy *policy)
 static void stp_policy_release(struct config_item *item)
 {
 	struct stp_policy *policy = to_stp_policy(item);
+	struct stm_device *stm = policy->stm;
 
+	/* a policy *can* be unbound and still exist in configfs tree */
+	if (!stm)
+		return;
+
+	mutex_lock(&stm->policy_mutex);
 	stp_policy_unbind(policy);
+	mutex_unlock(&stm->policy_mutex);
+
 	kfree(policy);
 }
 
-- 
2.7.0