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authorPaul Moore <paul@paul-moore.com>2018-02-20 09:52:38 -0500
committerPaul Moore <paul@paul-moore.com>2018-02-23 11:22:22 -0500
commitce423631ce1f20564f818e7de6bc0eee0c01badd (patch)
tree8af35df7e249950085f24e6842b6d0058c6893c7 /kernel/audit.c
parent23138ead270045f1b3e912e667967b6094244999 (diff)
downloadlinux-ce423631ce1f20564f818e7de6bc0eee0c01badd.tar.bz2
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>
Diffstat (limited to 'kernel/audit.c')
-rw-r--r--kernel/audit.c66
1 files changed, 55 insertions, 11 deletions
diff --git a/kernel/audit.c b/kernel/audit.c
index 2de74be7cef5..1a3e75d9a66c 100644
--- 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 &&