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

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Message-Id: <1477926701-14782-1-git-send-email-maarten@treewalker.org>
Date:   Mon, 31 Oct 2016 16:11:41 +0100
From:   Maarten ter Huurne <maarten@...ewalker.org>
To:     Vinod Koul <vinod.koul@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        dmaengine@...r.kernel.org, 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 | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 8971370..84c6e88 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -1223,6 +1223,11 @@ 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);
-- 
2.6.6