linux-kernel - [PATCH] dma-debug: Avoid NULL dereference when checking sync

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Message-Id: <1456672859-15521-1-git-send-email-maarten@treewalker.org>
Date:	Sun, 28 Feb 2016 16:20:59 +0100
From:	Maarten ter Huurne <maarten@...ewalker.org>
To:	Dan Williams <dan.j.williams@...el.com>,
	Jiri Kosina <jkosina@...e.cz>
Cc:	linux-kernel@...r.kernel.org,
	Maarten ter Huurne <maarten@...ewalker.org>
Subject: [PATCH] dma-debug: Avoid NULL dereference when checking sync

check_sync() calls bucket_find_contain(), which in turn calls
dma_get_max_seg_size(), which dereferences the device pointer.

Signed-off-by: Maarten ter Huurne <maarten@...ewalker.org>
---
 lib/dma-debug.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 4a1515f..4960402 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -1194,6 +1194,13 @@ static void check_sync(struct device *dev,
 	struct hash_bucket *bucket;
 	unsigned long flags;
 
+	if (!ref->dev) {
+		err_printk(dev, NULL, "DMA-API: device driver passes NULL "
+				"for device to DMA sync function; "
+				"cannot check usage\n");
+		return;
+	}
+
 	bucket = get_hash_bucket(ref, &flags);
 
 	entry = bucket_find_contain(&bucket, ref, &flags);
-- 
2.6.2