linux-kernel - [PATCH] SMACK: Add missing rcu_read_lock/unlock for process capability walk.

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Date:	Wed, 20 Apr 2011 15:00:44 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	jmorris@...ei.org
Cc:	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH] SMACK: Add missing rcu_read_lock/unlock for process capability walk.

From: Andi Kleen <ak@...ux.intel.com>

smk_access_entry does a RCU list walk for a list shared with other
threads. It relies on the caller doing rcu_read_lock().
One caller forgot to do to this, which could lead to races
on preemptible kernels.

Move the rcu_read_lock() into smk_access_entry instead.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 security/smack/smack_access.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index 7b0d3b3..43b20f3 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -92,6 +92,7 @@ int smk_access_entry(char *subject_label, char *object_label,
 	int may = -ENOENT;
 	struct smack_rule *srp;
 
+	rcu_read_lock();
 	list_for_each_entry_rcu(srp, rule_list, list) {
 		if (srp->smk_subject == subject_label ||
 		    strcmp(srp->smk_subject, subject_label) == 0) {
@@ -102,6 +103,7 @@ int smk_access_entry(char *subject_label, char *object_label,
 			}
 		}
 	}
+	rcu_read_unlock();
 
 	return may;
 }
@@ -184,9 +186,7 @@ int smk_access_flags(char *subject_label, char *object_label, int request,
 	 * good. A negative response from smk_access_entry()
 	 * indicates there is no entry for this pair.
 	 */
-	rcu_read_lock();
 	may = smk_access_entry(subject_label, object_label, &smack_rule_list);
-	rcu_read_unlock();
 
 	if (may > 0 && (request & may) == request)
 		goto out_audit;
-- 
1.7.4.2

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