5.4-stable review patch. If anyone has any objections, please let me know.
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From: Albin Babu Varghese albinbabuvarghese20@gmail.com
[ 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 --- drivers/video/fbdev/core/bitblit.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)
diff --git a/drivers/video/fbdev/core/bitblit.c b/drivers/video/fbdev/core/bitblit.c index 99a4f048b96ac..75c20f8e58e33 100644 --- a/drivers/video/fbdev/core/bitblit.c +++ b/drivers/video/fbdev/core/bitblit.c @@ -169,6 +169,11 @@ 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) @@ -182,6 +187,18 @@ 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;