linux-kernel - [PATCH net-next v1] net: devmem: NULL check netdev_nl_get_dma

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Message-ID: <20250829220003.3310242-1-almasrymina@google.com>
Date: Fri, 29 Aug 2025 21:59:38 +0000
From: Mina Almasry <almasrymina@...gle.com>
To: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Mina Almasry <almasrymina@...gle.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>, Joe Damato <jdamato@...tly.com>, 
	Stanislav Fomichev <sdf@...ichev.me>
Subject: [PATCH net-next v1] net: devmem: NULL check netdev_nl_get_dma_dev
 return value

netdev_nl_get_dma_dev can return NULL. This happens in the unlikely
scenario that netdev->dev.parent is NULL, or all the calls to the
ndo_queue_get_dma_dev return NULL from the driver.

Current code doesn't NULL check the return value, so it may be passed to
net_devmem_bind_dmabuf, which AFAICT will eventually hit
WARN_ON(!dmabuf || !dev) in dma_buf_dynamic_attach and do a kernel
splat. Avoid this scenario by using IS_ERR_OR_NULL in place of IS_ERR.

Found by code inspection.

Note that this was a problem even before the fixes patch, since we
passed netdev->dev.parent to net_devmem_bind_dmabuf before NULL checking
it anyway :( But that code got removed in the fixes patch (and retained
the bug).

Fixes: b8aab4bb9585 ("net: devmem: allow binding on rx queues with same DMA devices")
Signed-off-by: Mina Almasry <almasrymina@...gle.com>

---
 net/core/netdev-genl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index 470fabbeacd9..779bcdb5653d 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -1098,7 +1098,7 @@ int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
 	dma_dev = netdev_queue_get_dma_dev(netdev, 0);
 	binding = net_devmem_bind_dmabuf(netdev, dma_dev, DMA_TO_DEVICE,
 					 dmabuf_fd, priv, info->extack);
-	if (IS_ERR(binding)) {
+	if (IS_ERR_OR_NULL(binding)) {
 		err = PTR_ERR(binding);
 		goto err_unlock_netdev;
 	}

base-commit: 4f54dff818d7b5b1d84becd5d90bc46e6233c0d7
-- 
2.51.0.318.gd7df087d1a-goog