2019-07-30 14:02:54

by Chuhong Yuan

Subject: [PATCH] drm/modes: Fix unterminated strncpy

strncpy(dest, src, strlen(src)) leads to unterminated
dest, which is dangerous.
Fix it by using strscpy.

Signed-off-by: Chuhong Yuan <[email protected]>
---
drivers/gpu/drm/drm_modes.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index 80fcd5dc1558..170fc24e0f31 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1770,7 +1770,7 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
}

if (named_mode) {
- strncpy(mode->name, name, mode_end);
+ strscpy(mode->name, name, mode_end + 1);
} else {
ret = drm_mode_parse_cmdline_res_mode(name, mode_end,
parse_extras,
--
2.20.1

2019-07-30 18:10:29

by Sean Paul

Subject: Re: [PATCH] drm/modes: Fix unterminated strncpy

On Tue, Jul 30, 2019 at 04:40:32PM +0800, Chuhong Yuan wrote:
> strncpy(dest, src, strlen(src)) leads to unterminated
> dest, which is dangerous.
> Fix it by using strscpy.
>
> Signed-off-by: Chuhong Yuan <[email protected]>
> ---
> drivers/gpu/drm/drm_modes.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index 80fcd5dc1558..170fc24e0f31 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -1770,7 +1770,7 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
> }
>
> if (named_mode) {
> - strncpy(mode->name, name, mode_end);
> + strscpy(mode->name, name, mode_end + 1);

Shouldn't you be checking that mode_end + 1 is not > than the size of mode->name
(ie: DRM_DISPLAY_MODE_LEN)? This still seems unsafe.

Sean

> } else {
> ret = drm_mode_parse_cmdline_res_mode(name, mode_end,
> parse_extras,
> --
> 2.20.1
>

--
Sean Paul, Software Engineer, Google / Chromium OS