[PATCH] drm/gud: validate TV mode names before creating enum property

[Tao Yu]

The GUD protocol returns TV mode names as fixed-size
GUD_CONNECTOR_TV_MODE_NAME_LEN entries and requires each name to be
NUL-terminated.

gud_connector_add_tv_mode() currently passes each fixed-size entry
directly to drm_mode_create_tv_properties_legacy(), which eventually
reaches drm_property_add_enum() and strlen(). If a device returns an
entry without a terminating NUL byte, strlen() reads past the end of
the slot and can run beyond the allocated buffer, triggering an
out-of-bounds read.

Validate that each returned TV mode name contains a NUL terminator
within its fixed-size slot before passing it to the DRM property code.
If a malformed entry is found, reject the device response with -EIO.

This fixes the out-of-bounds read without changing the handling of
valid devices, and avoids silently truncating malformed protocol data.

Reported-by: syzbot+9ae8e7...@syzkaller.appspotmail.com
Fixes: 40e1a70b4aed ("drm: Add GUD USB Display driver")
Signed-off-by: Tao Yu <tao...@intel.com>
---
drivers/gpu/drm/gud/gud_connector.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/gud/gud_connector.c b/drivers/gpu/drm/gud/gud_connector.c
index ea0cca58b7c89..8141c3a1e30ad 100644
--- a/drivers/gpu/drm/gud/gud_connector.c
+++ b/drivers/gpu/drm/gud/gud_connector.c
@@ -396,8 +396,16 @@ static int gud_connector_add_tv_mode(struct gud_device *gdrm, struct drm_connect
}

num_modes = ret / GUD_CONNECTOR_TV_MODE_NAME_LEN;
- for (i = 0; i < num_modes; i++)
- modes[i] = &buf[i * GUD_CONNECTOR_TV_MODE_NAME_LEN];
+ for (i = 0; i < num_modes; i++) {
+ char *mode = &buf[i * GUD_CONNECTOR_TV_MODE_NAME_LEN];
+
+ if (!memchr(mode, '\0', GUD_CONNECTOR_TV_MODE_NAME_LEN)) {
+ ret = -EIO;
+ goto free;
+ }
+
+ modes[i] = mode;
+ }

ret = drm_mode_create_tv_properties_legacy(connector->dev, num_modes, modes);
free:
--
2.34.1