Re: [PATCH] video/hdmi: Change strncpy() into memcpy() in hdmi_spd_infoframe_init

On Fri, Jan 18, 2019 at 8:51 PM Joe Perches [off-list ref] wrote:

On Fri, 2019-01-18 at 20:32 +0100, Mathieu Malaterre wrote:

quoted

Using strncpy() is less than perfect since the destination buffers do not
need to be NUL terminated. Replace strncpy() with memcpy() to address a
warning triggered by gcc using W=1 and optimize the code a bit.

This commit removes the following warnings:

  drivers/video/hdmi.c:234:2: warning: 'strncpy' specified bound 8 equals destination size [-Wstringop-truncation]
  drivers/video/hdmi.c:235:2: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]

[]

quoted

diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c

[]

quoted

@@ -231,8 +231,8 @@ int hdmi_spd_infoframe_init(struct hdmi_spd_infoframe *frame,
      frame->version = 1;
      frame->length = HDMI_SPD_INFOFRAME_SIZE;

-     strncpy(frame->vendor, vendor, sizeof(frame->vendor));
-     strncpy(frame->product, product, sizeof(frame->product));
+     memcpy(frame->vendor, vendor, sizeof(frame->vendor));
+     memcpy(frame->product, product, sizeof(frame->product));

This is not good.

vendor can be any location and shorter than sizeof(frame->vendor)
so this can copy from invalid memory locations.

Ah right. I did not realize that and know I see the call with "Intel",
will re-spin.

You probably want strscpy.

Right.

This is called with at least "mediatek" and "broadcom", so perhaps
it's better still to change the struct vendor size to something a
bit larger.  Maybe change vendor[8] to vendor[16];

Looks like 8 bytes is required for call like hdmi_spd_infoframe_unpack()

include/linux/hdmi.h:struct hdmi_spd_infoframe {
include/linux/hdmi.h-   enum hdmi_infoframe_type type;
include/linux/hdmi.h-   unsigned char version;
include/linux/hdmi.h-   unsigned char length;
include/linux/hdmi.h-   char vendor[8];
include/linux/hdmi.h-   char product[16];
include/linux/hdmi.h-   enum hdmi_spd_sdi sdi;
include/linux/hdmi.h-};