[PATCH v2] staging: fbtft: prefer snprintf over sprintf in fbtft-core.c

[PATCH v2] staging: fbtft: prefer snprintf over sprintf in fbtft-core.c

[Tomasz Unger]

Using sprintf has potential for buffer overflows if the formatted
string exceeds the destination buffer size. Replace it with
snprintf, passing sizeof() of the fixed-size stack buffers
(text1[50] and text2[50]) so the write is always bounded.

An overflow is impossible here: even the worst case for the
argument types (size_t for text1, three ints for text2) still
fits within 50 bytes. Use snprintf() rather than scnprintf()
since the return value is not used here.

Signed-off-by: Tomasz Unger <tomasz.unger@yahoo.pl>
---
Changes in v2 (per Dan Carpenter's review):
- Switched from scnprintf() to snprintf(), since the return
  value is unused.
- Reworded the commit message: overflow is impossible, not
  merely unlikely, and dropped detail about where the values
  come from.

Verified with checkpatch.pl - no errors or warnings.
Compiled the fbtft module successfully with CONFIG_FB_TFT=m.
fb.ko, syscopyarea.ko, sysimgblt.ko, sysfillrect.ko,
fb_sys_fops.ko and fbtft.ko all load without errors in a QEMU
environment (verified via insmod and lsmod, dmesg shows no
errors).
---
 drivers/staging/fbtft/fbtft-core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
index ca0c38221c16..9ea0442a337e 100644
--- a/drivers/staging/fbtft/fbtft-core.c
+++ b/drivers/staging/fbtft/fbtft-core.c
@@ -784,10 +784,10 @@ int fbtft_register_framebuffer(struct fb_info *fb_info)
 	fbtft_sysfs_init(par);
 
 	if (par->txbuf.buf && par->txbuf.len >= 1024)
-		sprintf(text1, ", %zu KiB buffer memory", par->txbuf.len >> 10);
+		snprintf(text1, sizeof(text1), ", %zu KiB buffer memory", par->txbuf.len >> 10);
 	if (spi)
-		sprintf(text2, ", spi%d.%d at %d MHz", spi->controller->bus_num,
-			spi_get_chipselect(spi, 0), spi->max_speed_hz / 1000000);
+		snprintf(text2, sizeof(text2), ", spi%d.%d at %d MHz", spi->controller->bus_num,
+			 spi_get_chipselect(spi, 0), spi->max_speed_hz / 1000000);
 	fb_dbg(fb_info,
 	       "%s frame buffer, %dx%d, %d KiB video memory%s, fps=%lu%s\n",
 	       fb_info->fix.id, fb_info->var.xres, fb_info->var.yres,

---
base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
change-id: 20260820-fbtft-v2-final-7891edd1d87e

Best regards,
--  
Tomasz Unger <tomasz.unger@yahoo.pl>

Re: [PATCH v2] staging: fbtft: prefer snprintf over sprintf in fbtft-core.c

[Andy Shevchenko]

On Thu, Aug 20, 2026 at 06:58:12PM +0200, Tomasz Unger wrote:
> Using sprintf has potential for buffer overflows if the formatted

sprintf()

> string exceeds the destination buffer size. Replace it with
> snprintf, passing sizeof() of the fixed-size stack buffers

snprintf()

> (text1[50] and text2[50]) so the write is always bounded.
> 
> An overflow is impossible here: even the worst case for the
> argument types (size_t for text1, three ints for text2) still
> fits within 50 bytes. Use snprintf() rather than scnprintf()
> since the return value is not used here.

Then why the patch is needed at all? Do you have any compiler that warns
you about something?

...

It looks like you ignored all my comments against v1...

-- 
With Best Regards,
Andy Shevchenko