fbdev: imxfb: Check fb_add_videomode to prevent null-ptr-deref

fb_add_videomode() can fail with -ENOMEM when its internal kmalloc() cannot
allocate a struct fb_modelist.  If that happens, the modelist stays empty but
the driver continues to register.  Add a check for its return value to prevent
poteintial null-ptr-deref, which is similar to the commit 17186f1 ("fbdev:
Fix do_register_framebuffer to prevent null-ptr-deref in fb_videomode_to_var").

Fixes: 1b6c793 ("video: imxfb: Add DT support")
Signed-off-by: Chenyuan Yang <chenyuan0y@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>

Author: WhiteFox-Project

drivers/video/fbdev/imxfb.c

@@ -996,8 +996,13 @@ static int imxfb_probe(struct platform_device *pdev)
 	info->fix.smem_start = fbi->map_dma;
 
 	INIT_LIST_HEAD(&info->modelist);
-	for (i = 0; i < fbi->num_modes; i++)
-		fb_add_videomode(&fbi->mode[i].mode, &info->modelist);
+	for (i = 0; i < fbi->num_modes; i++) {
+		ret = fb_add_videomode(&fbi->mode[i].mode, &info->modelist);
+		if (ret) {
+			dev_err(&pdev->dev, "Failed to add videomode\n");
+			goto failed_cmap;
+		}
+	}
 
 	/*
 	 * This makes sure that our colour bitfield