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+48b0652a95834717f...@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=48b0652a95834717f190 Suggested-by: Helge Deller <del...@gmx.de> Tested-by: syzbot+48b0652a95834717f...@syzkaller.appspotmail.com Signed-off-by: Albin Babu Varghese <albinbabuvarghes...@gmail.com> --- Changes in v2: - Partially render when height exceeding screen boundaries instead of skipping - Update character count when width is clipped to prevent buffer mismatch Link to v1: https://lore.kernel.org/all/20250927075010.119671-1-albinbabuvarghes...@gmail.com/ --- drivers/video/fbdev/core/bitblit.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/drivers/video/fbdev/core/bitblit.c b/drivers/video/fbdev/core/bitblit.c index f9475c14f733..116b4bf5e94c 100644 --- a/drivers/video/fbdev/core/bitblit.c +++ b/drivers/video/fbdev/core/bitblit.c @@ -160,6 +160,11 @@ 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) @@ -173,6 +178,21 @@ 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; -- 2.51.0
