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[1.160.233.238]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-361410bafa9sm7114296a91.15.2026.04.19.03.01.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 19 Apr 2026 03:01:37 -0700 (PDT) From: Sean Chang To: Benjamin Coddington Cc: Jeff Layton , trondmy@kernel.org, anna@kernel.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, Sean Chang Subject: [PATCH v2 2/2] NFS: Fix RCU dereference of cl_xprt in nfs_compare_super_address Date: Sun, 19 Apr 2026 18:01:28 +0800 Message-ID: <20260419100128.20546-3-seanwascoding@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260419100128.20546-1-seanwascoding@gmail.com> References: <20260419100128.20546-1-seanwascoding@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The cl_xprt pointer in struct rpc_clnt is marked as __rcu. Accessing it directly in nfs_compare_super_address() is unsafe and triggers Sparse warnings. Fix this by wrapping the access with rcu_read_lock() and using rcu_dereference() to safely retrieve the transport pointer. This ensures the xprt structure remains memory-safe during the comparison of network namespaces and addresses. Additionally, add a check for the XPRT_CONNECTED state bit. While RCU guarantees the memory remains valid, checking XPRT_CONNECTED ensures the transport is still logically active, preventing operations on a transport that is already undergoing teardown. Fixes: 7e3fcf61abde ("nfs: don't share mounts between network namespaces") Signed-off-by: Sean Chang --- fs/nfs/super.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/fs/nfs/super.c b/fs/nfs/super.c index 7a318581f85b..c9044d9d64cc 100644 --- a/fs/nfs/super.c +++ b/fs/nfs/super.c @@ -1166,12 +1166,23 @@ static int nfs_set_super(struct super_block *s, struct fs_context *fc) static int nfs_compare_super_address(struct nfs_server *server1, struct nfs_server *server2) { + struct rpc_xprt *xprt1, *xprt2; struct sockaddr *sap1, *sap2; - struct rpc_xprt *xprt1 = server1->client->cl_xprt; - struct rpc_xprt *xprt2 = server2->client->cl_xprt; + + rcu_read_lock(); + + xprt1 = rcu_dereference(server1->client->cl_xprt); + xprt2 = rcu_dereference(server2->client->cl_xprt); + + if (!xprt1 || !xprt2 || + !test_bit(XPRT_CONNECTED, &xprt1->state) || + !test_bit(XPRT_CONNECTED, &xprt2->state)) + goto out_unlock; if (!net_eq(xprt1->xprt_net, xprt2->xprt_net)) - return 0; + goto out_unlock; + + rcu_read_unlock(); sap1 = (struct sockaddr *)&server1->nfs_client->cl_addr; sap2 = (struct sockaddr *)&server2->nfs_client->cl_addr; @@ -1203,6 +1214,10 @@ static int nfs_compare_super_address(struct nfs_server *server1, } return 1; + +out_unlock: + rcu_read_unlock(); + return 0; } static int nfs_compare_userns(const struct nfs_server *old, -- 2.43.0