ftrace: Get a reference counter for the trace_array on filter files

The ftrace set_ftrace_filter and set_ftrace_notrace files are specific for
an instance now. They need to take a reference to the instance otherwise
there could be a race between accessing the files and deleting the instance.

It wasn't until the :mod: caching where these file operations started
referencing the trace_array directly.

Cc: stable@vger.kernel.org
Fixes: 673feb9d76ab3 ("ftrace: Add :mod: caching infrastructure to trace_array")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 18 insertions, 9 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 62a50bf399d6..32c2eb167de0 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3540,21 +3540,22 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
         struct ftrace_hash *hash;
         struct list_head *mod_head;
         struct trace_array *tr = ops->private;
-        int ret = 0;
+        int ret = -ENOMEM;
 
         ftrace_ops_init(ops);
 
         if (unlikely(ftrace_disabled))
                 return -ENODEV;
 
+        if (tr && trace_array_get(tr) < 0)
+                return -ENODEV;
+
         iter = kzalloc(sizeof(*iter), GFP_KERNEL);
         if (!iter)
-                return -ENOMEM;
+                goto out;
 
-        if (trace_parser_get_init(&iter->parser, FTRACE_BUFF_MAX)) {
-                kfree(iter);
-                return -ENOMEM;
-        }
+        if (trace_parser_get_init(&iter->parser, FTRACE_BUFF_MAX))
+                goto out;
 
         iter->ops = ops;
         iter->flags = flag;
@@ -3584,13 +3585,13 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
 
                 if (!iter->hash) {
                         trace_parser_put(&iter->parser);
-                        kfree(iter);
-                        ret = -ENOMEM;
                         goto out_unlock;
                 }
         } else
                 iter->hash = hash;
 
+        ret = 0;
+
         if (file->f_mode & FMODE_READ) {
                 iter->pg = ftrace_pages_start;
 
@@ -3602,7 +3603,6 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
                         /* Failed */
                         free_ftrace_hash(iter->hash);
                         trace_parser_put(&iter->parser);
-                        kfree(iter);
                 }
         } else
                 file->private_data = iter;
@@ -3610,6 +3610,13 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
  out_unlock:
         mutex_unlock(&ops->func_hash->regex_lock);
 
+ out:
+        if (ret) {
+                kfree(iter);
+                if (tr)
+                        trace_array_put(tr);
+        }
+
         return ret;
 }
 
@@ -5037,6 +5044,8 @@ int ftrace_regex_release(struct inode *inode, struct file *file)
 
         mutex_unlock(&iter->ops->func_hash->regex_lock);
         free_ftrace_hash(iter->hash);
+        if (iter->tr)
+                trace_array_put(iter->tr);
         kfree(iter);
 
         return 0;