[PATCH] video: fbdev: fix potential OOB read in fast_imageblit()

From: Zhang Shurong
Date: Sat Jun 24 2023 - 12:18:30 EST


There is a potential OOB read at fast_imageblit, for
"colortab[(*src >> 4)]" can become a negative value due to
"const char *s = image->data, *src".
This change makes sure the index for colortab always positive
or zero.

Similar commit:
https://patchwork.kernel.org/patch/11746067

Potential bug report:
https://groups.google.com/g/syzkaller-bugs/c/9ubBXKeKXf4/m/k-QXy4UgAAAJ

Signed-off-by: Zhang Shurong <zhang_shurong@xxxxxxxxxxx>
---
drivers/video/fbdev/core/sysimgblt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/sysimgblt.c b/drivers/video/fbdev/core/sysimgblt.c
index 335e92b813fc..665ef7a0a249 100644
--- a/drivers/video/fbdev/core/sysimgblt.c
+++ b/drivers/video/fbdev/core/sysimgblt.c
@@ -189,7 +189,7 @@ static void fast_imageblit(const struct fb_image *image, struct fb_info *p,
u32 fgx = fgcolor, bgx = bgcolor, bpp = p->var.bits_per_pixel;
u32 ppw = 32/bpp, spitch = (image->width + 7)/8;
u32 bit_mask, eorx, shift;
- const char *s = image->data, *src;
+ const u8 *s = image->data, *src;
u32 *dst;
const u32 *tab;
size_t tablen;
--
2.41.0