[PATCH v2] iio: backend: fix out-of-bound write

Markus Burri
2025-05-05T04:54:25Z

The buffer is set to 80 character. If a caller write more characters,
count is truncated to the max available space in "simple_write_to_buffer".
But afterwards a string terminator is written to the buffer at offset count
without boundary check. The zero termination is written OUT-OF-BOUND.

Add a check that the given buffer is smaller then the buffer to prevent.

Fixes: 035b4989211d ("iio: backend: make sure to NULL terminate stack buffer")
Signed-off-by: Markus Burri <markus.burri@mt.com>
---
drivers/iio/industrialio-backend.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
index a43c8d1bb3d0..31fe793e345e 100644
--- a/drivers/iio/industrialio-backend.c
+++ b/drivers/iio/industrialio-backend.c
@@ -155,11 +155,14 @@ static ssize_t iio_backend_debugfs_write_reg(struct file *file,
ssize_t rc;
int ret;

+ if (count >= sizeof(buf))
+ return -ENOSPC;
+
rc = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf, count);
if (rc < 0)
return rc;

- buf[count] = '\0';
+ buf[rc] = '\0';

ret = sscanf(buf, "%i %i", &back->cached_reg_addr, &val);

base-commit: b4432656b36e5cc1d50a1f2dc15357543add530e
--
2.39.5