staging/fbtft: Remove all strcpy() uses

strcpy() performs no bounds checking on the destination buffer. This
could result in linear overflows beyond the end of the buffer, leading
to all kinds of misbehaviors. The safe replacement is strscpy() but in
this case it is simpler to add NULL to the first position since we want
to empty the string.

This is a previous step in the path to remove the strcpy() function.

Signed-off-by: Len Baker <redacted>
---
 drivers/staging/fbtft/fbtft-core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
index 3723269890d5..b8791806cb20 100644
--- a/drivers/staging/fbtft/fbtft-core.c
+++ b/drivers/staging/fbtft/fbtft-core.c

@@ -1037,7 +1037,7 @@ int fbtft_init_display(struct fbtft_par *par)
 		case -1:
 			i++;
 			/* make debug message */
-			strcpy(msg, "");
+			msg[0] = 0;
 			j = i + 1;
 			while (par->init_sequence[j] >= 0) {
 				sprintf(str, "0x%02X ", par->init_sequence[j]);
--

2.25.1

On Sun, Jul 18, 2021 at 4:43 PM Len Baker [off-list ref] wrote:

strcpy() performs no bounds checking on the destination buffer. This
could result in linear overflows beyond the end of the buffer, leading
to all kinds of misbehaviors. The safe replacement is strscpy() but in
this case it is simpler to add NULL to the first position since we want
to empty the string.

This is a previous step in the path to remove the strcpy() function.

Any document behind this (something to read on the site(s) more or
less affiliated with what is going to happen in the kernel) to read
background?

...

Strictly speaking it should be '\0'.

                        j = i + 1;
                        while (par->init_sequence[j] >= 0) {
                                sprintf(str, "0x%02X ", par->init_sequence[j]);

-- 
With Best Regards,
Andy Shevchenko

On Sun, Jul 18, 2021 at 9:43 PM Andy Shevchenko
[off-list ref] wrote:

On Sun, Jul 18, 2021 at 4:43 PM Len Baker [off-list ref] wrote:

quoted

strcpy() performs no bounds checking on the destination buffer. This
could result in linear overflows beyond the end of the buffer, leading
to all kinds of misbehaviors. The safe replacement is strscpy() but in
this case it is simpler to add NULL to the first position since we want

"NULL" is a pointer value, "NUL" is the character with value zero.

quoted

to empty the string.

quoted

This is a previous step in the path to remove the strcpy() function.

Any document behind this (something to read on the site(s) more or
less affiliated with what is going to happen in the kernel) to read
background?

...

quoted

                case -1:
                        i++;
                        /* make debug message */
-                       strcpy(msg, "");

While this strcpy() is provably safe at compile-time, and will probably
be replaced by an assignment to zero by the compiler...

quoted

+                       msg[0] = 0;

Strictly speaking it should be '\0'.

quoted

                        j = i + 1;
                        while (par->init_sequence[j] >= 0) {
                                sprintf(str, "0x%02X ", par->init_sequence[j]);

... the real danger is the

        strcat(msg, str);

on the next line.
Fortunately this whole debug printing block (including the strcpy)
can (and should) be rewritten to just use "%*ph".

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Hi,

On Sun, Jul 18, 2021 at 10:42:42PM +0300, Andy Shevchenko wrote:

On Sun, Jul 18, 2021 at 4:43 PM Len Baker [off-list ref] wrote:

quoted

strcpy() performs no bounds checking on the destination buffer. This
could result in linear overflows beyond the end of the buffer, leading
to all kinds of misbehaviors. The safe replacement is strscpy() but in
this case it is simpler to add NULL to the first position since we want
to empty the string.

quoted

This is a previous step in the path to remove the strcpy() function.

Any document behind this (something to read on the site(s) more or
less affiliated with what is going to happen in the kernel) to read
background?

This is a task of the KSPP (kernel self protection project) [1]

[1] https://github.com/KSPP/linux/issues/88

...

quoted

                case -1:
                        i++;
                        /* make debug message */
-                       strcpy(msg, "");
+                       msg[0] = 0;

Strictly speaking it should be '\0'.

Ok, understood.

quoted

                        j = i + 1;
                        while (par->init_sequence[j] >= 0) {
                                sprintf(str, "0x%02X ", par->init_sequence[j]);

--
With Best Regards,
Andy Shevchenko

Thanks for the feedback,
Len

On Mon, Jul 19, 2021 at 09:53:29AM +0200, Geert Uytterhoeven wrote:

On Sun, Jul 18, 2021 at 9:43 PM Andy Shevchenko
[off-list ref] wrote:

quoted

On Sun, Jul 18, 2021 at 4:43 PM Len Baker [off-list ref] wrote:

quoted

strcpy() performs no bounds checking on the destination buffer. This
could result in linear overflows beyond the end of the buffer, leading
to all kinds of misbehaviors. The safe replacement is strscpy() but in
this case it is simpler to add NULL to the first position since we want

"NULL" is a pointer value, "NUL" is the character with value zero.

Ok, understood. Thanks.

quoted

quoted

to empty the string.

quoted

This is a previous step in the path to remove the strcpy() function.

Any document behind this (something to read on the site(s) more or
less affiliated with what is going to happen in the kernel) to read
background?

...

quoted

                case -1:
                        i++;
                        /* make debug message */
-                       strcpy(msg, "");

While this strcpy() is provably safe at compile-time, and will probably
be replaced by an assignment to zero by the compiler...

quoted

quoted

+                       msg[0] = 0;

Strictly speaking it should be '\0'.

quoted

                        j = i + 1;
                        while (par->init_sequence[j] >= 0) {
                                sprintf(str, "0x%02X ", par->init_sequence[j]);

... the real danger is the

        strcat(msg, str);

on the next line.
Fortunately this whole debug printing block (including the strcpy)
can (and should) be rewritten to just use "%*ph".

Ok, I will work on it and I will send a v2 for review. Thanks for the
feedback.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Regards,
Len