linux-kernel - [PATCH] drm/etnaviv: fix memory leak when mapping prime imported buffers

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Message-Id: <1589969500-6554-1-git-send-email-martin.fuzzey@flowbird.group>
Date:   Wed, 20 May 2020 12:10:02 +0200
From:   Martin Fuzzey <martin.fuzzey@...wbird.group>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     stable@...r.kernel.org,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        etnaviv@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/etnaviv: fix memory leak when mapping prime imported buffers

When using mmap() on a prime imported buffer allocated by a
different driver (such as imx-drm) the later munmap() does
not correctly decrement the refcount of the original enaviv_gem_object,
leading to a leak.

Signed-off-by: Martin Fuzzey <martin.fuzzey@...wbird.group>
Cc: stable@...r.kernel.org
---
 drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
index f24dd21..28a01b8 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
@@ -93,7 +93,25 @@ static void *etnaviv_gem_prime_vmap_impl(struct etnaviv_gem_object *etnaviv_obj)
 static int etnaviv_gem_prime_mmap_obj(struct etnaviv_gem_object *etnaviv_obj,
 		struct vm_area_struct *vma)
 {
-	return dma_buf_mmap(etnaviv_obj->base.dma_buf, vma, 0);
+	int ret;
+
+	ret = dma_buf_mmap(etnaviv_obj->base.dma_buf, vma, 0);
+
+	/* drm_gem_mmap_obj() has already been called before this function
+	 * and has incremented our refcount, expecting it to be decremented
+	 * on unmap() via drm_gem_vm_close().
+	 * However dma_buf_mmap() invokes drm_gem_cma_prime_mmap()
+	 * that ends up updating the vma->vma_private_data to point to the
+	 * dma_buf's gem object.
+	 * Hence our gem object here will not have its refcount decremented
+	 * when userspace does unmap().
+	 * So decrement the refcount here to avoid a memory leak if the dma
+	 * buf mapping was successful.
+	 */
+	if (!ret)
+		drm_gem_object_put_unlocked(&etnaviv_obj->base);
+
+	return ret;
 }
 
 static const struct etnaviv_gem_ops etnaviv_gem_prime_ops = {
-- 
1.9.1