tracing: Get trace_array reference for available_tracers files

As instances may have different tracers available, we need to look at the
trace_array descriptor that shows the list of the available tracers for the
instance. But there's a race between opening the file and an admin
deleting the instance. The trace_array_get() needs to be called before
accessing the trace_array.

Cc: stable@vger.kernel.org
Fixes: 607e2ea167e56 ("tracing: Set up infrastructure to allow tracers for instances")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 15 insertions, 2 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 252f79c435f8..fa7d813b04c6 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4355,9 +4355,14 @@ static int show_traces_open(struct inode *inode, struct file *file)
         if (tracing_disabled)
                 return -ENODEV;
 
+        if (trace_array_get(tr) < 0)
+                return -ENODEV;
+
         ret = seq_open(file, &show_traces_seq_ops);
-        if (ret)
+        if (ret) {
+                trace_array_put(tr);
                 return ret;
+        }
 
         m = file->private_data;
         m->private = tr;
@@ -4365,6 +4370,14 @@ static int show_traces_open(struct inode *inode, struct file *file)
         return 0;
 }
 
+static int show_traces_release(struct inode *inode, struct file *file)
+{
+        struct trace_array *tr = inode->i_private;
+
+        trace_array_put(tr);
+        return seq_release(inode, file);
+}
+
 static ssize_t
 tracing_write_stub(struct file *filp, const char __user *ubuf,
                    size_t count, loff_t *ppos)
@@ -4395,8 +4408,8 @@ static const struct file_operations tracing_fops = {
 static const struct file_operations show_traces_fops = {
         .open           = show_traces_open,
         .read           = seq_read,
-        .release        = seq_release,
         .llseek         = seq_lseek,
+        .release        = show_traces_release,
 };
 
 static ssize_t