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fbdev: fix potential OOB read in fast_imageblit()

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commit c2d22806aecb24e2de55c30a06e5d6eb297d161d upstream.

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@foxmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Zhang Shurong 2023-06-25 00:16:49 +08:00 committed by Greg Kroah-Hartman
parent e6bbad7571
commit cae8542495
1 changed files with 1 additions and 1 deletions
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2
drivers/video/fbdev/core/sysimgblt.c
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@ -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;