iommu: apple-dart: fix potential null pointer deref

If kzalloc() fails, accessing cfg->supports_bypass causes a null pointer dereference.

Fix by checking for NULL immediately after allocation and returning -ENOMEM.

Fixes: 3bc0102 ("iommu: apple-dart: Allow mismatched bypass support")
Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Link: https://lore.kernel.org/r/20250314230102.11008-1-qasdev00@gmail.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: qasim-ijaz

drivers/iommu/apple-dart.c

@@ -797,12 +797,11 @@ static int apple_dart_of_xlate(struct device *dev,
 
 	if (!cfg) {
 		cfg = kzalloc(sizeof(*cfg), GFP_KERNEL);
-
+		if (!cfg)
+			return -ENOMEM;
 		/* Will be ANDed with DART capabilities */
 		cfg->supports_bypass = true;
 	}
-	if (!cfg)
-		return -ENOMEM;
 	dev_iommu_priv_set(dev, cfg);
 
 	cfg_dart = cfg->stream_maps[0].dart;