audit: track the owner of the command mutex ourselves

Evidently the __mutex_owner() function was never intended for use
outside the core mutex code, so build a thing locking wrapper around
the mutex code which allows us to track the mutex owner.

One, arguably positive, side effect is that this allows us to hide
the audit_cmd_mutex inside of kernel/audit.c behind the lock/unlock
functions.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/kernel/audit.c b/kernel/audit.c
index 2de74be..1a3e75d 100644 (file)
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -181,9 +181,21 @@ static char *audit_feature_names[2] = {
        "loginuid_immutable",
 };
 
-
-/* Serialize requests from userspace. */
-DEFINE_MUTEX(audit_cmd_mutex);
+/**
+ * struct audit_ctl_mutex - serialize requests from userspace
+ * @lock: the mutex used for locking
+ * @owner: the task which owns the lock
+ *
+ * Description:
+ * This is the lock struct used to ensure we only process userspace requests
+ * in an orderly fashion.  We can't simply use a mutex/lock here because we
+ * need to track lock ownership so we don't end up blocking the lock owner in
+ * audit_log_start() or similar.
+ */
+static struct audit_ctl_mutex {
+       struct mutex lock;
+       void *owner;
+} audit_cmd_mutex;
 
 /* AUDIT_BUFSIZ is the size of the temporary buffer used for formatting
  * audit records.  Since printk uses a 1024 byte buffer, this buffer
@@ -228,6 +240,36 @@ int auditd_test_task(struct task_struct *task)
 }
 
 /**
+ * audit_ctl_lock - Take the audit control lock
+ */
+void audit_ctl_lock(void)
+{
+       mutex_lock(&audit_cmd_mutex.lock);
+       audit_cmd_mutex.owner = current;
+}
+
+/**
+ * audit_ctl_unlock - Drop the audit control lock
+ */
+void audit_ctl_unlock(void)
+{
+       audit_cmd_mutex.owner = NULL;
+       mutex_unlock(&audit_cmd_mutex.lock);
+}
+
+/**
+ * audit_ctl_owner_current - Test to see if the current task owns the lock
+ *
+ * Description:
+ * Return true if the current task owns the audit control lock, false if it
+ * doesn't own the lock.
+ */
+static bool audit_ctl_owner_current(void)
+{
+       return (current == audit_cmd_mutex.owner);
+}
+
+/**
  * auditd_pid_vnr - Return the auditd PID relative to the namespace
  *
  * Description:
@@ -861,8 +903,8 @@ int audit_send_list(void *_dest)
        struct sock *sk = audit_get_sk(dest->net);
 
        /* wait for parent to finish and send an ACK */
-       mutex_lock(&audit_cmd_mutex);
-       mutex_unlock(&audit_cmd_mutex);
+       audit_ctl_lock();
+       audit_ctl_unlock();
 
        while ((skb = __skb_dequeue(&dest->q)) != NULL)
                netlink_unicast(sk, skb, dest->portid, 0);
@@ -903,8 +945,8 @@ static int audit_send_reply_thread(void *arg)
        struct audit_reply *reply = (struct audit_reply *)arg;
        struct sock *sk = audit_get_sk(reply->net);
 
-       mutex_lock(&audit_cmd_mutex);
-       mutex_unlock(&audit_cmd_mutex);
+       audit_ctl_lock();
+       audit_ctl_unlock();
 
        /* Ignore failure. It'll only happen if the sender goes away,
           because our timeout is set to infinite. */
@@ -1469,7 +1511,7 @@ static void audit_receive(struct sk_buff  *skb)
        nlh = nlmsg_hdr(skb);
        len = skb->len;
 
-       mutex_lock(&audit_cmd_mutex);
+       audit_ctl_lock();
        while (nlmsg_ok(nlh, len)) {
                err = audit_receive_msg(skb, nlh);
                /* if err or if this message says it wants a response */
@@ -1478,7 +1520,7 @@ static void audit_receive(struct sk_buff  *skb)
 
                nlh = nlmsg_next(nlh, &len);
        }
-       mutex_unlock(&audit_cmd_mutex);
+       audit_ctl_unlock();
 }
 
 /* Run custom bind function on netlink socket group connect or bind requests. */
@@ -1550,6 +1592,9 @@ static int __init audit_init(void)
        for (i = 0; i < AUDIT_INODE_BUCKETS; i++)
                INIT_LIST_HEAD(&audit_inode_hash[i]);
 
+       mutex_init(&audit_cmd_mutex.lock);
+       audit_cmd_mutex.owner = NULL;
+
        pr_info("initializing netlink subsys (%s)\n",
                audit_default ? "enabled" : "disabled");
        register_pernet_subsys(&audit_net_ops);
@@ -1713,8 +1758,7 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
         *    using a PID anchored in the caller's namespace
         * 2. generator holding the audit_cmd_mutex - we don't want to block
         *    while holding the mutex */
-       if (!(auditd_test_task(current) ||
-             (current == __mutex_owner(&audit_cmd_mutex)))) {
+       if (!(auditd_test_task(current) || audit_ctl_owner_current())) {
                long stime = audit_backlog_wait_time;
 
                while (audit_backlog_limit &&

diff --git a/kernel/audit.h b/kernel/audit.h
index af5bc59..214e149 100644 (file)
--- a/kernel/audit.h
+++ b/kernel/audit.h
@@ -341,4 +341,5 @@ extern struct list_head *audit_killed_trees(void);
 #define audit_filter_inodes(t,c) AUDIT_DISABLED
 #endif
 
-extern struct mutex audit_cmd_mutex;
+extern void audit_ctl_lock(void);
+extern void audit_ctl_unlock(void);

diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
index fd35312..67e6956 100644 (file)
--- a/kernel/audit_tree.c
+++ b/kernel/audit_tree.c
@@ -709,7 +709,7 @@ static int prune_tree_thread(void *unused)
                        schedule();
                }
 
-               mutex_lock(&audit_cmd_mutex);
+               audit_ctl_lock();
                mutex_lock(&audit_filter_mutex);
 
                while (!list_empty(&prune_list)) {
@@ -727,7 +727,7 @@ static int prune_tree_thread(void *unused)
                }
 
                mutex_unlock(&audit_filter_mutex);
-               mutex_unlock(&audit_cmd_mutex);
+               audit_ctl_unlock();
        }
        return 0;
 }
@@ -924,7 +924,7 @@ static void audit_schedule_prune(void)
  */
 void audit_kill_trees(struct list_head *list)
 {
-       mutex_lock(&audit_cmd_mutex);
+       audit_ctl_lock();
        mutex_lock(&audit_filter_mutex);
 
        while (!list_empty(list)) {
@@ -942,7 +942,7 @@ void audit_kill_trees(struct list_head *list)
        }
 
        mutex_unlock(&audit_filter_mutex);
-       mutex_unlock(&audit_cmd_mutex);
+       audit_ctl_unlock();
 }
 
 /*