[PATCH 5.15.y] SUNRPC: lock against ->sock changing during sysfs read

[Robert Garcia]

From: NeilBrown <neilb@xxxxxxx>

[ Upstream commit b49ea673e119f59c71645e2f65b3ccad857c90ee ]

->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@xxxxxxx>
Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
Signed-off-by: Robert Garcia <rob_garcia@xxxxxxx>
---
 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 55da1b627a7d..83ba1f2adf62 100644
--- a/net/sunrpc/sysfs.c
+++ b/net/sunrpc/sysfs.c
@@ -113,11 +113,14 @@ static ssize_t rpc_sysfs_xprt_srcaddr_show(struct kobject *kobj,
 		return 0;
 
 	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 9e122c20fcc6..07acc6845ce2 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -1680,7 +1680,12 @@ 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);
 
-- 
2.34.1