The patch below does not apply to the 4.11-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 48d0e023af9799cd7220335baf8e3ba61eeafbeb Mon Sep 17 00:00:00 2001
From: Paul Moore <paul@xxxxxxxxxxxxxx>
Date: Tue, 2 May 2017 10:16:05 -0400
Subject: [PATCH] audit: fix the RCU locking for the auditd_connection
structure
Cong Wang correctly pointed out that the RCU read locking of the
auditd_connection struct was wrong, this patch correct this by
adopting a more traditional, and correct RCU locking model.
This patch is heavily based on an earlier prototype by Cong Wang.
Cc: <stable@xxxxxxxxxxxxxxx> # 4.11.x-
Reported-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx>
diff --git a/kernel/audit.c b/kernel/audit.c
index 10bc2bad2adf..a7c6a50477aa 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -112,18 +112,19 @@ struct audit_net {
* @pid: auditd PID
* @portid: netlink portid
* @net: the associated network namespace
- * @lock: spinlock to protect write access
+ * @rcu: RCU head
*
* Description:
* This struct is RCU protected; you must either hold the RCU lock for reading
- * or the included spinlock for writing.
+ * or the associated spinlock for writing.
*/
static struct auditd_connection {
struct pid *pid;
u32 portid;
struct net *net;
- spinlock_t lock;
-} auditd_conn;
+ struct rcu_head rcu;
+} *auditd_conn = NULL;
+static DEFINE_SPINLOCK(auditd_conn_lock);
/* If audit_rate_limit is non-zero, limit the rate of sending audit records
* to that number per second. This prevents DoS attacks, but results in
@@ -215,9 +216,11 @@ struct audit_reply {
int auditd_test_task(struct task_struct *task)
{
int rc;
+ struct auditd_connection *ac;
rcu_read_lock();
- rc = (auditd_conn.pid && auditd_conn.pid == task_tgid(task) ? 1 : 0);
+ ac = rcu_dereference(auditd_conn);
+ rc = (ac && ac->pid == task_tgid(task) ? 1 : 0);
rcu_read_unlock();
return rc;
@@ -225,22 +228,21 @@ int auditd_test_task(struct task_struct *task)
/**
* auditd_pid_vnr - Return the auditd PID relative to the namespace
- * @auditd: the auditd connection
*
* Description:
- * Returns the PID in relation to the namespace, 0 on failure. This function
- * takes the RCU read lock internally, but if the caller needs to protect the
- * auditd_connection pointer it should take the RCU read lock as well.
+ * Returns the PID in relation to the namespace, 0 on failure.
*/
-static pid_t auditd_pid_vnr(const struct auditd_connection *auditd)
+static pid_t auditd_pid_vnr(void)
{
pid_t pid;
+ const struct auditd_connection *ac;
rcu_read_lock();
- if (!auditd || !auditd->pid)
+ ac = rcu_dereference(auditd_conn);
+ if (!ac || !ac->pid)
pid = 0;
else
- pid = pid_vnr(auditd->pid);
+ pid = pid_vnr(ac->pid);
rcu_read_unlock();
return pid;
@@ -434,6 +436,24 @@ static int audit_set_failure(u32 state)
}
/**
+ * auditd_conn_free - RCU helper to release an auditd connection struct
+ * @rcu: RCU head
+ *
+ * Description:
+ * Drop any references inside the auditd connection tracking struct and free
+ * the memory.
+ */
+ static void auditd_conn_free(struct rcu_head *rcu)
+ {
+ struct auditd_connection *ac;
+
+ ac = container_of(rcu, struct auditd_connection, rcu);
+ put_pid(ac->pid);
+ put_net(ac->net);
+ kfree(ac);
+ }
+
+/**
* auditd_set - Set/Reset the auditd connection state
* @pid: auditd PID
* @portid: auditd netlink portid
@@ -441,27 +461,33 @@ static int audit_set_failure(u32 state)
*
* Description:
* This function will obtain and drop network namespace references as
- * necessary.
+ * necessary. Returns zero on success, negative values on failure.
*/
-static void auditd_set(struct pid *pid, u32 portid, struct net *net)
+static int auditd_set(struct pid *pid, u32 portid, struct net *net)
{
unsigned long flags;
+ struct auditd_connection *ac_old, *ac_new;
- spin_lock_irqsave(&auditd_conn.lock, flags);
- if (auditd_conn.pid)
- put_pid(auditd_conn.pid);
- if (pid)
- auditd_conn.pid = get_pid(pid);
- else
- auditd_conn.pid = NULL;
- auditd_conn.portid = portid;
- if (auditd_conn.net)
- put_net(auditd_conn.net);
- if (net)
- auditd_conn.net = get_net(net);
- else
- auditd_conn.net = NULL;
- spin_unlock_irqrestore(&auditd_conn.lock, flags);
+ if (!pid || !net)
+ return -EINVAL;
+
+ ac_new = kzalloc(sizeof(*ac_new), GFP_KERNEL);
+ if (!ac_new)
+ return -ENOMEM;
+ ac_new->pid = get_pid(pid);
+ ac_new->portid = portid;
+ ac_new->net = get_net(net);
+
+ spin_lock_irqsave(&auditd_conn_lock, flags);
+ ac_old = rcu_dereference_protected(auditd_conn,
+ lockdep_is_held(&auditd_conn_lock));
+ rcu_assign_pointer(auditd_conn, ac_new);
+ spin_unlock_irqrestore(&auditd_conn_lock, flags);
+
+ if (ac_old)
+ call_rcu(&ac_old->rcu, auditd_conn_free);
+
+ return 0;
}
/**
@@ -556,13 +582,19 @@ static void kauditd_retry_skb(struct sk_buff *skb)
*/
static void auditd_reset(void)
{
+ unsigned long flags;
struct sk_buff *skb;
+ struct auditd_connection *ac_old;
/* if it isn't already broken, break the connection */
- rcu_read_lock();
- if (auditd_conn.pid)
- auditd_set(0, 0, NULL);
- rcu_read_unlock();
+ spin_lock_irqsave(&auditd_conn_lock, flags);
+ ac_old = rcu_dereference_protected(auditd_conn,
+ lockdep_is_held(&auditd_conn_lock));
+ rcu_assign_pointer(auditd_conn, NULL);
+ spin_unlock_irqrestore(&auditd_conn_lock, flags);
+
+ if (ac_old)
+ call_rcu(&ac_old->rcu, auditd_conn_free);
/* flush all of the main and retry queues to the hold queue */
while ((skb = skb_dequeue(&audit_retry_queue)))
@@ -588,6 +620,7 @@ static int auditd_send_unicast_skb(struct sk_buff *skb)
u32 portid;
struct net *net;
struct sock *sk;
+ struct auditd_connection *ac;
/* NOTE: we can't call netlink_unicast while in the RCU section so
* take a reference to the network namespace and grab local
@@ -597,15 +630,15 @@ static int auditd_send_unicast_skb(struct sk_buff *skb)
* section netlink_unicast() should safely return an error */
rcu_read_lock();
- if (!auditd_conn.pid) {
+ ac = rcu_dereference(auditd_conn);
+ if (!ac) {
rcu_read_unlock();
rc = -ECONNREFUSED;
goto err;
}
- net = auditd_conn.net;
- get_net(net);
+ net = get_net(ac->net);
sk = audit_get_sk(net);
- portid = auditd_conn.portid;
+ portid = ac->portid;
rcu_read_unlock();
rc = netlink_unicast(sk, skb, portid, 0);
@@ -740,6 +773,7 @@ static int kauditd_thread(void *dummy)
u32 portid = 0;
struct net *net = NULL;
struct sock *sk = NULL;
+ struct auditd_connection *ac;
#define UNICAST_RETRIES 5
@@ -747,14 +781,14 @@ static int kauditd_thread(void *dummy)
while (!kthread_should_stop()) {
/* NOTE: see the lock comments in auditd_send_unicast_skb() */
rcu_read_lock();
- if (!auditd_conn.pid) {
+ ac = rcu_dereference(auditd_conn);
+ if (!ac) {
rcu_read_unlock();
goto main_queue;
}
- net = auditd_conn.net;
- get_net(net);
+ net = get_net(ac->net);
sk = audit_get_sk(net);
- portid = auditd_conn.portid;
+ portid = ac->portid;
rcu_read_unlock();
/* attempt to flush the hold queue */
@@ -1117,7 +1151,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
s.failure = audit_failure;
/* NOTE: use pid_vnr() so the PID is relative to the current
* namespace */
- s.pid = auditd_pid_vnr(&auditd_conn);
+ s.pid = auditd_pid_vnr();
s.rate_limit = audit_rate_limit;
s.backlog_limit = audit_backlog_limit;
s.lost = atomic_read(&audit_lost);
@@ -1160,7 +1194,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
/* test the auditd connection */
audit_replace(req_pid);
- auditd_pid = auditd_pid_vnr(&auditd_conn);
+ auditd_pid = auditd_pid_vnr();
/* only the current auditd can unregister itself */
if ((!new_pid) && (new_pid != auditd_pid)) {
audit_log_config_change("audit_pid", new_pid,
@@ -1174,19 +1208,30 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
return -EEXIST;
}
- if (audit_enabled != AUDIT_OFF)
- audit_log_config_change("audit_pid", new_pid,
- auditd_pid, 1);
-
if (new_pid) {
/* register a new auditd connection */
- auditd_set(req_pid, NETLINK_CB(skb).portid,
- sock_net(NETLINK_CB(skb).sk));
+ err = auditd_set(req_pid,
+ NETLINK_CB(skb).portid,
+ sock_net(NETLINK_CB(skb).sk));
+ if (audit_enabled != AUDIT_OFF)
+ audit_log_config_change("audit_pid",
+ new_pid,
+ auditd_pid,
+ err ? 0 : 1);
+ if (err)
+ return err;
+
/* try to process any backlog */
wake_up_interruptible(&kauditd_wait);
- } else
+ } else {
+ if (audit_enabled != AUDIT_OFF)
+ audit_log_config_change("audit_pid",
+ new_pid,
+ auditd_pid, 1);
+
/* unregister the auditd connection */
auditd_reset();
+ }
}
if (s.mask & AUDIT_STATUS_RATE_LIMIT) {
err = audit_set_rate_limit(s.rate_limit);
@@ -1454,10 +1499,11 @@ static void __net_exit audit_net_exit(struct net *net)
{
struct audit_net *aunet = net_generic(net, audit_net_id);
- rcu_read_lock();
- if (net == auditd_conn.net)
- auditd_reset();
- rcu_read_unlock();
+ /* NOTE: you would think that we would want to check the auditd
+ * connection and potentially reset it here if it lives in this
+ * namespace, but since the auditd connection tracking struct holds a
+ * reference to this namespace (see auditd_set()) we are only ever
+ * going to get here after that connection has been released */
netlink_kernel_release(aunet->sk);
}
@@ -1481,9 +1527,6 @@ static int __init audit_init(void)
sizeof(struct audit_buffer),
0, SLAB_PANIC, NULL);
- memset(&auditd_conn, 0, sizeof(auditd_conn));
- spin_lock_init(&auditd_conn.lock);
-
skb_queue_head_init(&audit_queue);
skb_queue_head_init(&audit_retry_queue);
skb_queue_head_init(&audit_hold_queue);