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Subject: [PATCH 23/23] SUNRPC: lock against ->sock changing during sysfs read
From:   NeilBrown <neilb@suse.de>
To:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Chuck Lever <chuck.lever@oracle.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>,
        Christoph Hellwig <hch@infradead.org>,
        David Howells <dhowells@redhat.com>
Cc:     linux-nfs@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Date:   Mon, 24 Jan 2022 14:48:32 +1100
Message-ID: <164299611287.26253.6282866540933339893.stgit@noble.brown>
In-Reply-To: <164299573337.26253.7538614611220034049.stgit@noble.brown>
References: <164299573337.26253.7538614611220034049.stgit@noble.brown>
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->sock can be set to NULL asynchronously unless ->recv_mutex is held.
So it is important to hold that mutex.  Otherwise a sysfs read can
trigger an oops.
Commit 17f09d3f619a ("SUNRPC: Check if the xprt is connected before
handling sysfs reads") appears to attempt to fix this problem, but it
only narrows the race window.

Fixes: 17f09d3f619a ("SUNRPC: Check if the xprt is connected before handling sysfs reads")
Fixes: a8482488a7d6 ("SUNRPC query transport's source port")
Signed-off-by: NeilBrown <neilb@suse.de>
---
 net/sunrpc/sysfs.c    |    5 ++++-
 net/sunrpc/xprtsock.c |    7 ++++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/sysfs.c b/net/sunrpc/sysfs.c
index 2766dd21935b..baaf65ea9e38 100644
--- a/net/sunrpc/sysfs.c
+++ b/net/sunrpc/sysfs.c
@@ -115,11 +115,14 @@ static ssize_t rpc_sysfs_xprt_srcaddr_show(struct kobject *kobj,
 	}
 
 	sock = container_of(xprt, struct sock_xprt, xprt);
-	if (kernel_getsockname(sock->sock, (struct sockaddr *)&saddr) < 0)
+	mutex_lock(&sock->recv_mutex);
+	if (sock->sock == NULL ||
+	    kernel_getsockname(sock->sock, (struct sockaddr *)&saddr) < 0)
 		goto out;
 
 	ret = sprintf(buf, "%pISc\n", &saddr);
 out:
+	mutex_unlock(&sock->recv_mutex);
 	xprt_put(xprt);
 	return ret + 1;
 }
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 9d34c71004fa..3f2b766e9f82 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -1641,7 +1641,12 @@ static int xs_get_srcport(struct sock_xprt *transport)
 unsigned short get_srcport(struct rpc_xprt *xprt)
 {
 	struct sock_xprt *sock = container_of(xprt, struct sock_xprt, xprt);
-	return xs_sock_getport(sock->sock);
+	unsigned short ret = 0;
+	mutex_lock(&sock->recv_mutex);
+	if (sock->sock)
+		ret = xs_sock_getport(sock->sock);
+	mutex_unlock(&sock->recv_mutex);
+	return ret;
 }
 EXPORT_SYMBOL(get_srcport);