[PATCH 5.4 46/60] net: rmnet: do not allow to change mux id if mux id is duplicated

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Taehee Yoo <ap420073@gmail.com>

[ Upstream commit 1dc49e9d164cd7e11c81279c83db84a147e14740 ]

Basically, duplicate mux id isn't be allowed.
So, the creation of rmnet will be failed if there is duplicate mux id
is existing.
But, changelink routine doesn't check duplicate mux id.

Test commands:
    modprobe rmnet
    ip link add dummy0 type dummy
    ip link add rmnet0 link dummy0 type rmnet mux_id 1
    ip link add rmnet1 link dummy0 type rmnet mux_id 2
    ip link set rmnet1 type rmnet mux_id 1

Fixes: 23790ef12082 ("net: qualcomm: rmnet: Allow to configure flags for existing devices")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
index 0ad64aa665925..3c0e6d24d0834 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
@@ -306,6 +306,10 @@ static int rmnet_changelink(struct net_device *dev, struct nlattr *tb[],
 
 	if (data[IFLA_RMNET_MUX_ID]) {
 		mux_id = nla_get_u16(data[IFLA_RMNET_MUX_ID]);
+		if (rmnet_get_endpoint(port, mux_id)) {
+			NL_SET_ERR_MSG_MOD(extack, "MUX ID already exists");
+			return -EINVAL;
+		}
 		ep = rmnet_get_endpoint(port, priv->mux_id);
 		if (!ep)
 			return -ENODEV;
-- 
2.20.1