truncation in drivers/video/fbdev/neofb.c

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* truncation in drivers/video/fbdev/neofb.c
@ 2023-08-29 16:45 Nick Desaulniers
  2023-08-29 17:11 ` Helge Deller
  0 siblings, 1 reply; 6+ messages in thread
From: Nick Desaulniers @ 2023-08-29 16:45 UTC (permalink / raw)
  To: Helge Deller
  Cc: linux-fbdev, dri-devel, clang-built-linux, LKML, Andrew Morton,
	Nathan Chancellor

Helge,
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]
drivers/video/fbdev/neofb.c:1963:3: warning: 'snprintf' will always be
truncated; specified size is 16, but format string expands to at least
18 [-Wfortify-source]
drivers/video/fbdev/neofb.c:1967:3: warning: 'snprintf' will always be
truncated; specified size is 16, but format string expands to at least
17 [-Wfortify-source]
drivers/video/fbdev/neofb.c:1971:3: warning: 'snprintf' will always be
truncated; specified size is 16, but format string expands to at least
17 [-Wfortify-source]
drivers/video/fbdev/neofb.c:1978:3: warning: 'snprintf' will always be
truncated; specified size is 16, but format string expands to at least
18 [-Wfortify-source]
drivers/video/fbdev/neofb.c:1985:3: warning: 'snprintf' will always be
truncated; specified size is 16, but format string expands to at least
17 [-Wfortify-source]
drivers/video/fbdev/neofb.c:1992:3: warning: 'snprintf' will always be
truncated; specified size is 16, but format string expands to at least
18 [-Wfortify-source]

https://github.com/ClangBuiltLinux/linux/issues/1923

Clang is right here.  `info->fix.id` is declared as `char id[16];` so
indeed string literals like "MagicGraph 256AV+" indeed lead to
truncation. But this is declared in include/uapi/linux/fb.h; I assume
those headers cant be changed? Can the strings be shortened then? Is
it perhaps time to delete this driver?

I see AKPM mentioned alluded to this in
commit 0e90454 ("neofb: avoid overwriting fb_info fields")

(Also, snprintf probably isn't necessary for string literals that
don't contain format strings)
-- 
Thanks,
~Nick Desaulniers

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: truncation in drivers/video/fbdev/neofb.c
  2023-08-29 16:45 truncation in drivers/video/fbdev/neofb.c Nick Desaulniers
@ 2023-08-29 17:11 ` Helge Deller
  2023-08-31 21:23   ` Helge Deller
  0 siblings, 1 reply; 6+ messages in thread
From: Helge Deller @ 2023-08-29 17:11 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: linux-fbdev, dri-devel, clang-built-linux, LKML, Andrew Morton,
	Nathan Chancellor

On 8/29/23 18:45, Nick Desaulniers wrote:
> Helge,
> 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]
> drivers/video/fbdev/neofb.c:1963:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 18 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1967:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 17 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1971:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 17 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1978:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 18 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1985:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 17 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1992:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 18 [-Wfortify-source]
>
> https://github.com/ClangBuiltLinux/linux/issues/1923
>
> Clang is right here.  `info->fix.id` is declared as `char id[16];` so
> indeed string literals like "MagicGraph 256AV+" indeed lead to
> truncation. But this is declared in include/uapi/linux/fb.h; I assume
> those headers cant be changed? Can the strings be shortened then? Is
> it perhaps time to delete this driver?
>
> I see AKPM mentioned alluded to this in
> commit 0e90454 ("neofb: avoid overwriting fb_info fields")
>
> (Also, snprintf probably isn't necessary for string literals that
> don't contain format strings)

It's just an ID field, so I don't think we need the full name of the card.
So using strscpy() and shorten the name, e.g. "MagicGr. 256XL+"
instead of "MagicGraph 256XL+" is probably the most simple solution?

Anyone want to send a patch?

Helge

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: truncation in drivers/video/fbdev/neofb.c
  2023-08-29 17:11 ` Helge Deller
@ 2023-08-31 21:23   ` Helge Deller
  2023-08-31 21:41     ` Nick Desaulniers
  0 siblings, 1 reply; 6+ messages in thread
From: Helge Deller @ 2023-08-31 21:23 UTC (permalink / raw)
  To: Nick Desaulniers, linux-fbdev, dri-devel, clang-built-linux, LKML,
	Andrew Morton, Nathan Chancellor

* Helge Deller <deller@gmx.de>:
> 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.

Helge

From: Helge Deller <deller@gmx.de>
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@gmx.de>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/all/CAKwvOdn0xoVWjQ6ufM_rojtKb0f1i1hW-J_xYGfKDNFdHwaeHQ@mail.gmail.com/
Link: https://github.com/ClangBuiltLinux/linux/issues/1923

diff --git a/drivers/video/fbdev/neofb.c b/drivers/video/fbdev/neofb.c
index d2f622b4c372..b905fe93b525 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, "MagicGraph256AV+", 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, "MagicGraph256XL+", sizeof(info->fix.id));
 		info->flags |= FBINFO_HWACCEL_IMAGEBLIT |
 		               FBINFO_HWACCEL_COPYAREA |
                 	       FBINFO_HWACCEL_FILLRECT;

^ permalink raw reply related	[flat|nested] 6+ messages in thread

* Re: truncation in drivers/video/fbdev/neofb.c
  2023-08-31 21:23   ` Helge Deller
@ 2023-08-31 21:41     ` Nick Desaulniers
  2023-08-31 22:15       ` Helge Deller
  0 siblings, 1 reply; 6+ messages in thread
From: Nick Desaulniers @ 2023-08-31 21:41 UTC (permalink / raw)
  To: Helge Deller
  Cc: linux-fbdev, dri-devel, clang-built-linux, LKML, Andrew Morton,
	Nathan Chancellor, Kees Cook, Justin Stitt

On Thu, Aug 31, 2023 at 2:23 PM Helge Deller <deller@gmx.de> wrote:
>
> * Helge Deller <deller@gmx.de>:
> > 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.
>
> Helge
>
> From: Helge Deller <deller@gmx.de>
> 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@gmx.de>
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Reported-by: Nick Desaulniers <ndesaulniers@google.com>
> Link: https://lore.kernel.org/all/CAKwvOdn0xoVWjQ6ufM_rojtKb0f1i1hW-J_xYGfKDNFdHwaeHQ@mail.gmail.com/
> Link: https://github.com/ClangBuiltLinux/linux/issues/1923

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:

>
> diff --git a/drivers/video/fbdev/neofb.c b/drivers/video/fbdev/neofb.c
> index d2f622b4c372..b905fe93b525 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));

I see the Mag.Graph change here; I'm curious why MagicGraph256XL+
didn't need that, too?

MagicGraph128ZV+
MagicGraph256XL+

those look like the same number of characters; are they? Does this one
need the `.` change?

```
diff --git a/drivers/video/fbdev/neofb.c b/drivers/video/fbdev/neofb.c
index b905fe93b525..6b7836f7f809 100644
--- a/drivers/video/fbdev/neofb.c
+++ b/drivers/video/fbdev/neofb.c
@@ -1957,7 +1957,7 @@ static struct fb_info *neo_alloc_fb_info(struct
pci_dev *dev,
                strscpy(info->fix.id, "MagicGraph128ZV", sizeof(info->fix.id));
                break;
        case FB_ACCEL_NEOMAGIC_NM2097:
-               strscpy(info->fix.id, "Mag.Graph128ZV+", sizeof(info->fix.id));
+               strscpy(info->fix.id, "MagicGraph128ZV+", sizeof(info->fix.id));
                break;
        case FB_ACCEL_NEOMAGIC_NM2160:
                strscpy(info->fix.id, "MagicGraph128XD", sizeof(info->fix.id));

```
Builds without error for me.  Though I guess the compiler doesn't know
what strscpy is semantically.

Ah
MagicGraph128ZV+
MagicGraph256XL+

are both 17 characters. (16 literal characters + trailing NUL)

So MagicGraph256XL+ (and MagicGraph256AV+) below will fail to copy the
NUL from the source, then overwrite the `+` with NUL IIUC.

There's no ambiguity for MagicGraph256XL+, but now MagicGraph256AV+
would look like MagicGraph256AV which is another possible variant.

Then perhaps MagicGraph256XL+ MagicGraph256AV+ and below might need to change.

Sorry, initially it looked like a simple fix and I was ready to sign
off on it; I hope I'm mistaken.  Thank you for the patch, but do
consider sending it to the ML for review before committing.

>                 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, "MagicGraph256AV+", 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, "MagicGraph256XL+", sizeof(info->fix.id));
>                 info->flags |= FBINFO_HWACCEL_IMAGEBLIT |
>                                FBINFO_HWACCEL_COPYAREA |
>                                FBINFO_HWACCEL_FILLRECT;



-- 
Thanks,
~Nick Desaulniers

^ permalink raw reply related	[flat|nested] 6+ messages in thread

* Re: truncation in drivers/video/fbdev/neofb.c
  2023-08-31 21:41     ` Nick Desaulniers
@ 2023-08-31 22:15       ` Helge Deller
  2023-08-31 22:26         ` Nick Desaulniers
  0 siblings, 1 reply; 6+ messages in thread
From: Helge Deller @ 2023-08-31 22:15 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: linux-fbdev, dri-devel, clang-built-linux, LKML, Andrew Morton,
	Nathan Chancellor, Kees Cook, Justin Stitt

* Nick Desaulniers <ndesaulniers@google.com>:
> On Thu, Aug 31, 2023 at 2:23 PM Helge Deller <deller@gmx.de> wrote:
> >
> > * Helge Deller <deller@gmx.de>:
> > > 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@gmx.de>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/all/CAKwvOdn0xoVWjQ6ufM_rojtKb0f1i1hW-J_xYGfKDNFdHwaeHQ@mail.gmail.com/
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;

^ permalink raw reply related	[flat|nested] 6+ messages in thread

* Re: truncation in drivers/video/fbdev/neofb.c
  2023-08-31 22:15       ` Helge Deller
@ 2023-08-31 22:26         ` Nick Desaulniers
  0 siblings, 0 replies; 6+ messages in thread
From: Nick Desaulniers @ 2023-08-31 22:26 UTC (permalink / raw)
  To: Helge Deller
  Cc: linux-fbdev, dri-devel, clang-built-linux, LKML, Andrew Morton,
	Nathan Chancellor, Kees Cook, Justin Stitt

On Thu, Aug 31, 2023 at 3:16 PM Helge Deller <deller@gmx.de> wrote:
>
> * Nick Desaulniers <ndesaulniers@google.com>:
> > On Thu, Aug 31, 2023 at 2:23 PM Helge Deller <deller@gmx.de> wrote:
> > >
> > > * Helge Deller <deller@gmx.de>:
> > > > 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@gmx.de>
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Reported-by: Nick Desaulniers <ndesaulniers@google.com>
> Link: https://lore.kernel.org/all/CAKwvOdn0xoVWjQ6ufM_rojtKb0f1i1hW-J_xYGfKDNFdHwaeHQ@mail.gmail.com/
> Link: https://github.com/ClangBuiltLinux/linux/issues/1923

ah yeah LGTM

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

>
> 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;
>


-- 
Thanks,
~Nick Desaulniers

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2023-08-31 22:27 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2023-08-29 16:45 truncation in drivers/video/fbdev/neofb.c Nick Desaulniers
2023-08-29 17:11 ` Helge Deller
2023-08-31 21:23   ` Helge Deller
2023-08-31 21:41     ` Nick Desaulniers
2023-08-31 22:15       ` Helge Deller
2023-08-31 22:26         ` Nick Desaulniers

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