LinuxLists.cc - truncation in drivers/video/fbdev/neofb.c

2023-08-29 19:18:27

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

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

2023-09-01 12:27:18

by Helge Deller

[permalink] [raw]

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

* Nick Desaulniers <[email protected]>:
> On Thu, Aug 31, 2023 at 2:23 PM Helge Deller <[email protected]> wrote:
> >
> > * Helge Deller <[email protected]>:
> > > 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 <[email protected]>
Reported-by: Nathan Chancellor <[email protected]>
Reported-by: Nick Desaulniers <[email protected]>
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;

2023-09-01 16:16:42

by Helge Deller

[permalink] [raw]

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

* Helge Deller <[email protected]>:
> 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 <[email protected]>
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 <[email protected]>
Reported-by: Nathan Chancellor <[email protected]>
Reported-by: Nick Desaulniers <[email protected]>
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;

2023-09-05 16:07:25

by Nick Desaulniers

[permalink] [raw]

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

On Thu, Aug 31, 2023 at 3:16 PM Helge Deller <[email protected]> wrote:
>
> * Nick Desaulniers <[email protected]>:
> > On Thu, Aug 31, 2023 at 2:23 PM Helge Deller <[email protected]> wrote:
> > >
> > > * Helge Deller <[email protected]>:
> > > > 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 <[email protected]>
> Reported-by: Nathan Chancellor <[email protected]>
> Reported-by: Nick Desaulniers <[email protected]>
> 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 <[email protected]>

>
> 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