Re: [PATCH v2] nvme-tcp: Fix netns UAF introduced by commit 1be52169c348

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Christoph Hellwig <hch@lst.de>
Date: Mon, 7 Apr 2025 16:31:21 +0200
> I had another look at this patch, and it feels wrong to me.  I don't
> think we are supposed to create sockets triggered by activity in
> a network namespace in the global namespace even if they are indirectly
> created through the nvme interface.  But maybe I'm misunderstanding
> how network namespaces work, which is entirely possible.
> 
> So to avoid the failure I'd be tempted to instead revert commit
> 1be52169c348 until the problem is fully sorted out.

The followup patch is wrong, and the correct fix is to take a reference
to the netns by sk_net_refcnt_upgrade().

---8<---
diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 26c459f0198d..72d260201d8c 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -1803,6 +1803,8 @@ static int nvme_tcp_alloc_queue(struct nvme_ctrl *nctrl, int qid,
 		ret = PTR_ERR(sock_file);
 		goto err_destroy_mutex;
 	}
+
+	sk_net_refcnt_upgrade(queue->sock->sk);
 	nvme_tcp_reclassify_socket(queue->sock);
 
 	/* Single syn retry */
---8<---