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

[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+9ae8e7884e451eaed5b4@syzkaller.appspotmail.com
Fixes: 40e1a70b4aed ("drm: Add GUD USB Display driver")
Signed-off-by: Tao Yu <tao1.yu@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

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

[Ruben Wauters]

[-- Attachment #1: Type: text/plain, Size: 2364 bytes --]

On Wed, 2026-08-19 at 15:28 +0800, Tao Yu wrote:
> 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.

Hello, Thank you for the patch. An earlier patch that fixes this issue
has been merged, however, this does look like a better fix of the
issue, so I will apply this one over the other one, as this does not
truncate the data.
> 
> This fixes the out-of-bounds read without changing the handling of
> valid devices, and avoids silently truncating malformed protocol data.
> 
> Reported-by: syzbot+9ae8e7884e451eaed5b4@syzkaller.appspotmail.com
> Fixes: 40e1a70b4aed ("drm: Add GUD USB Display driver")
> Signed-off-by: Tao Yu <tao1.yu@intel.com>
Reviewed-by: Ruben Wauters <rubenru09@aol.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:

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 870 bytes --]