Re: truncation in drivers/video/fbdev/neofb.c

[Helge Deller]

* Nick Desaulniers <ndesaulniers@xxxxxxxxxx>:
> On Thu, Aug 31, 2023 at 2:23 PM Helge Deller <deller@xxxxxx> wrote:
> >
> > * Helge Deller <deller@xxxxxx>:
> > > On 8/29/23 18:45, Nick Desaulniers wrote:
> > > > A recent change in clang made it better about spotting snprintf that
> > > > will result in truncation.  Nathan reported the following instances:
> > > >
> > > > drivers/video/fbdev/neofb.c:1959:3: warning: 'snprintf' will always be
> > > > truncated; specified size is 16, but format string expands to at least
> > > > 17 [-Wfortify-source]
> >
> > FYI, I've added the patch below to the fbdev for-next git tree.
> > [...]
> 
> This indeed makes the warning go away, but that's more so due to the
> use of strscpy now rather than snprintf.  That alone is a good change
> but we still have definite truncation.  See below:
> [...]

Nick, thanks for your review and findings!
Now every string should be max. 15 chars (which fits with the trailing
NUL into the char[16] array).

Helge


Subject: [PATCH] fbdev: neofb: Shorten Neomagic product name in info struct

Avoid those compiler warnings:
neofb.c:1959:3: warning: 'snprintf' will always be truncated;
   specified size is 16, but format string expands to at least 17 [-Wfortify-source]

Signed-off-by: Helge Deller <deller@xxxxxx>
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Reported-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Link: https://lore.kernel.org/all/CAKwvOdn0xoVWjQ6ufM_rojtKb0f1i1hW-J_xYGfKDNFdHwaeHQ@xxxxxxxxxxxxxx/
Link: https://github.com/ClangBuiltLinux/linux/issues/1923

diff --git a/drivers/video/fbdev/neofb.c b/drivers/video/fbdev/neofb.c
index d2f622b4c372..b58b11015c0c 100644
--- a/drivers/video/fbdev/neofb.c
+++ b/drivers/video/fbdev/neofb.c
@@ -1948,49 +1948,40 @@ static struct fb_info *neo_alloc_fb_info(struct pci_dev *dev,
 
 	switch (info->fix.accel) {
 	case FB_ACCEL_NEOMAGIC_NM2070:
-		snprintf(info->fix.id, sizeof(info->fix.id),
-				"MagicGraph 128");
+		strscpy(info->fix.id, "MagicGraph128", sizeof(info->fix.id));
 		break;
 	case FB_ACCEL_NEOMAGIC_NM2090:
-		snprintf(info->fix.id, sizeof(info->fix.id),
-				"MagicGraph 128V");
+		strscpy(info->fix.id, "MagicGraph128V", sizeof(info->fix.id));
 		break;
 	case FB_ACCEL_NEOMAGIC_NM2093:
-		snprintf(info->fix.id, sizeof(info->fix.id),
-				"MagicGraph 128ZV");
+		strscpy(info->fix.id, "MagicGraph128ZV", sizeof(info->fix.id));
 		break;
 	case FB_ACCEL_NEOMAGIC_NM2097:
-		snprintf(info->fix.id, sizeof(info->fix.id),
-				"MagicGraph 128ZV+");
+		strscpy(info->fix.id, "Mag.Graph128ZV+", sizeof(info->fix.id));
 		break;
 	case FB_ACCEL_NEOMAGIC_NM2160:
-		snprintf(info->fix.id, sizeof(info->fix.id),
-				"MagicGraph 128XD");
+		strscpy(info->fix.id, "MagicGraph128XD", sizeof(info->fix.id));
 		break;
 	case FB_ACCEL_NEOMAGIC_NM2200:
-		snprintf(info->fix.id, sizeof(info->fix.id),
-				"MagicGraph 256AV");
+		strscpy(info->fix.id, "MagicGraph256AV", sizeof(info->fix.id));
 		info->flags |= FBINFO_HWACCEL_IMAGEBLIT |
 		               FBINFO_HWACCEL_COPYAREA |
                 	       FBINFO_HWACCEL_FILLRECT;
 		break;
 	case FB_ACCEL_NEOMAGIC_NM2230:
-		snprintf(info->fix.id, sizeof(info->fix.id),
-				"MagicGraph 256AV+");
+		strscpy(info->fix.id, "Mag.Graph256AV+", sizeof(info->fix.id));
 		info->flags |= FBINFO_HWACCEL_IMAGEBLIT |
 		               FBINFO_HWACCEL_COPYAREA |
                 	       FBINFO_HWACCEL_FILLRECT;
 		break;
 	case FB_ACCEL_NEOMAGIC_NM2360:
-		snprintf(info->fix.id, sizeof(info->fix.id),
-				"MagicGraph 256ZX");
+		strscpy(info->fix.id, "MagicGraph256ZX", sizeof(info->fix.id));
 		info->flags |= FBINFO_HWACCEL_IMAGEBLIT |
 		               FBINFO_HWACCEL_COPYAREA |
                 	       FBINFO_HWACCEL_FILLRECT;
 		break;
 	case FB_ACCEL_NEOMAGIC_NM2380:
-		snprintf(info->fix.id, sizeof(info->fix.id),
-				"MagicGraph 256XL+");
+		strscpy(info->fix.id, "Mag.Graph256XL+", sizeof(info->fix.id));
 		info->flags |= FBINFO_HWACCEL_IMAGEBLIT |
 		               FBINFO_HWACCEL_COPYAREA |
                 	       FBINFO_HWACCEL_FILLRECT;