[PATCH v1] gpio: fix potential out-of-bound write

[Markus Burri]

Check that the input size does not exceed the buffer size.
If a caller write more characters, count is truncated to the max available
space in "simple_write_to_buffer".
Write a zero termination afterwards.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202505091754.285hHbr2-lkp@xxxxxxxxx/
Signed-off-by: Markus Burri <markus.burri@xxxxxx>
---
 drivers/gpio/gpio-virtuser.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpio-virtuser.c b/drivers/gpio/gpio-virtuser.c
index 13407fd4f0eb..eab6726953b4 100644
--- a/drivers/gpio/gpio-virtuser.c
+++ b/drivers/gpio/gpio-virtuser.c
@@ -401,10 +401,15 @@ static ssize_t gpio_virtuser_direction_do_write(struct file *file,
 	char buf[32], *trimmed;
 	int ret, dir, val = 0;
 
-	ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
+	if (count >= sizeof(buf))
+		return -EINVAL;
+
+	ret = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, user_buf, count);
 	if (ret < 0)
 		return ret;
 
+	buf[ret] = '\0';
+
 	trimmed = strim(buf);
 
 	if (strcmp(trimmed, "input") == 0) {
@@ -623,12 +628,15 @@ static ssize_t gpio_virtuser_consumer_write(struct file *file,
 	char buf[GPIO_VIRTUSER_NAME_BUF_LEN + 2];
 	int ret;
 
+	if (count >= sizeof(buf))
+		return -EINVAL;
+
 	ret = simple_write_to_buffer(buf, GPIO_VIRTUSER_NAME_BUF_LEN, ppos,
 				     user_buf, count);
 	if (ret < 0)
 		return ret;
 
-	buf[strlen(buf) - 1] = '\0';
+	buf[ret] = '\0';
 
 	ret = gpiod_set_consumer_name(data->ad.desc, buf);
 	if (ret)

base-commit: 92a09c47464d040866cf2b4cd052bc60555185fb
-- 
2.39.5