fbdev: avoid vertical overflow when making space for the logo

fbcon_prepare_logo(): Avoid vertical overflow when making space for the logo
Signed-off-by: NGeert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: NGeoff Levand <geoffrey.levand@am.sony.com>
Acked-By: NJames Simmons <jsimmons@infradead.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/video/console/fbcon.c

@@ -618,8 +618,13 @@ static void fbcon_prepare_logo(struct vc_data *vc, struct fb_info *info,
 			r -= cols;
 		}
 		if (!save) {
-			vc->vc_y += logo_lines;
-			vc->vc_pos += logo_lines * vc->vc_size_row;
+			int lines;
+			if (vc->vc_y + logo_lines >= rows)
+				lines = rows - vc->vc_y - 1;
+			else
+				lines = logo_lines;
+			vc->vc_y += lines;
+			vc->vc_pos += lines * vc->vc_size_row;
 		}
 	}
 	scr_memsetw((unsigned short *) vc->vc_origin,