linux-kernel - [PATCH 1/5] debugfs: Prevent NULL dereference reading from string property

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Message-ID: <20230516160753.32317-2-rf@opensource.cirrus.com>
Date:   Tue, 16 May 2023 17:07:49 +0100
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     <gregkh@...uxfoundation.org>, <rafael@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <patches@...nsource.cirrus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: [PATCH 1/5] debugfs: Prevent NULL dereference reading from string property

Check in debugfs_read_file_str() if the string pointer is NULL.

It is perfectly reasonable that a driver may wish to export a string
to debugfs that can have the value NULL to indicate empty/unused/ignore.

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 fs/debugfs/file.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 1f971c880dde..2c085ab4e800 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -878,6 +878,9 @@ ssize_t debugfs_read_file_str(struct file *file, char __user *user_buf,
 		return ret;
 
 	str = *(char **)file->private_data;
+	if (!str)
+		return simple_read_from_buffer(user_buf, count, ppos, "\n", 1);
+
 	len = strlen(str) + 1;
 	copy = kmalloc(len, GFP_KERNEL);
 	if (!copy) {
-- 
2.30.2