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fbdev: Add bounds checking in bit_putcs to fix vmalloc-out-of-bounds

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[ Upstream commit 3637d34b35b287ab830e66048841ace404382b67 ]

Add bounds checking to prevent writes past framebuffer boundaries when
rendering text near screen edges. Return early if the Y position is off-screen
and clip image height to screen boundary. Break from the rendering loop if the
X position is off-screen. When clipping image width to fit the screen, update
the character count to match the clipped width to prevent buffer size
mismatches.

Without the character count update, bit_putcs_aligned and bit_putcs_unaligned
receive mismatched parameters where the buffer is allocated for the clipped
width but cnt reflects the original larger count, causing out-of-bounds writes.

Reported-by: syzbot+48b0652a95834717f190@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=48b0652a95834717f190
Suggested-by: Helge Deller <deller@gmx.de>
Tested-by: syzbot+48b0652a95834717f190@syzkaller.appspotmail.com
Signed-off-by: Albin Babu Varghese <albinbabuvarghese20@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Albin Babu Varghese
2025-10-03 03:32:09 -04:00
committed by Greg Kroah-Hartman
parent 81e829f699
commit 86df8ade88
1 changed files with 17 additions and 0 deletions
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17
drivers/video/fbdev/core/bitblit.c
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@@ -168,6 +168,11 @@ static void bit_putcs(struct vc_data *vc, struct fb_info *info,
image.height = vc->vc_font.height;
image.depth = 1;
if (image.dy >= info->var.yres)
return;
image.height = min(image.height, info->var.yres - image.dy);
if (attribute) {
buf = kmalloc(cellsize, GFP_ATOMIC);
if (!buf)
@@ -181,6 +186,18 @@ static void bit_putcs(struct vc_data *vc, struct fb_info *info,
cnt = count;
image.width = vc->vc_font.width * cnt;
if (image.dx >= info->var.xres)
break;
if (image.dx + image.width > info->var.xres) {
image.width = info->var.xres - image.dx;
cnt = image.width / vc->vc_font.width;
if (cnt == 0)
break;
image.width = cnt * vc->vc_font.width;
}
pitch = DIV_ROUND_UP(image.width, 8) + scan_align;
pitch &= ~scan_align;
size = pitch * image.height + buf_align;