[PATCH] tracing: Correct the refcount for hist/hist_debug file if single_open() fails

[Tengda Wu]

The function event_{hist,hist_debug}_open() maintains the refcount of
'file->tr' and 'file' through tracing_open_file_tr(), but it does not
roll back these counts when the subsequent single_open() call fails,
leading to a refcount leak.

A very obvious case is that if the hist/hist_debug file belongs to a
certain instance, the failure of single_open() will prevent the deletion
of that instance, as it relies on the condition 'tr->ref == 1' within
__remove_instance().

Fix this by calling tracing_release_file_tr() to correct the refcount
when single_open() fails.

Fixes: 1cc111b9cddc ("tracing: Fix uaf issue when open the hist or hist_debug file")
Signed-off-by: Tengda Wu <wutengda@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v6.7+
---
 kernel/trace/trace_events_hist.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index ad7419e24055..900b06fa8505 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5702,8 +5702,10 @@ static int event_hist_open(struct inode *inode, struct file *file)
 	/* Clear private_data to avoid warning in single_open() */
 	file->private_data = NULL;
 	ret = single_open(file, hist_show, hist_file);
-	if (ret)
+	if (ret) {
 		kfree(hist_file);
+		tracing_release_file_tr(inode, file);
+	}
 
 	return ret;
 }
@@ -5979,7 +5981,10 @@ static int event_hist_debug_open(struct inode *inode, struct file *file)
 
 	/* Clear private_data to avoid warning in single_open() */
 	file->private_data = NULL;
-	return single_open(file, hist_debug_show, file);
+	ret = single_open(file, hist_debug_show, file);
+	if (ret)
+		tracing_release_file_tr(inode, file);
+	return ret;
 }
 
 const struct file_operations event_hist_debug_fops = {
-- 
2.34.1