The patch allows non-root users to receive cn proc connector
notifications, as anyone can normally get process start/exit status from
/proc. The reason for not allowing non-root users to receive multicast
messages is long gone, as described in this thread:
https://linux-kernel.vger.kernel.narkive.com/CpJFcnra/multicast-netlink-for-non-root-process
Also, many other netlink protocols allow non-root users to receive multicast
messages, and there is no reason to discriminate against CONNECTOR.
Reason we need this change is we need to run our DB application as a
non-root user.
Signed-off-by: Anjali Kulkarni <anjali.k.kulkarni@oracle.com>
---
drivers/connector/cn_proc.c | 7 -------
drivers/connector/connector.c | 1 +
2 files changed, 1 insertion(+), 7 deletions(-)
diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
index ef3820b43b5c..03ba70f07113 100644
--- a/drivers/connector/cn_proc.c
+++ b/drivers/connector/cn_proc.c
@@ -376,12 +376,6 @@ static void cn_proc_mcast_ctl(struct cn_msg *msg,
!task_is_in_init_pid_ns(current))
return;
- /* Can only change if privileged. */
- if (!__netlink_ns_capable(nsp, &init_user_ns, CAP_NET_ADMIN)) {
- err = EPERM;
- goto out;
- }
-
if (msg->len == sizeof(mc_op))
mc_op = *((enum proc_cn_mcast_op *)msg->data);
else
@@ -414,7 +408,6 @@ static void cn_proc_mcast_ctl(struct cn_msg *msg,
break;
}
-out:
cn_proc_ack(err, msg->seq, msg->ack);
}
diff --git a/drivers/connector/connector.c b/drivers/connector/connector.c
index 1b7851b1aa0f..136a9f38a063 100644
--- a/drivers/connector/connector.c
+++ b/drivers/connector/connector.c
@@ -251,6 +251,7 @@ static int cn_init(void)
{
struct cn_dev *dev = &cdev;
struct netlink_kernel_cfg cfg = {
+ .flags = NL_CFG_F_NONROOT_RECV,
.groups = CN_NETLINK_USERS + 0xf,
.input = cn_rx_skb,
};
--
2.39.2On Wed, Mar 08, 2023 at 07:19:52PM -0800, Anjali Kulkarni wrote: > The patch allows non-root users to receive cn proc connector > notifications, as anyone can normally get process start/exit status from > /proc. The reason for not allowing non-root users to receive multicast > messages is long gone, as described in this thread: > https://linux-kernel.vger.kernel.narkive.com/CpJFcnra/multicast-netlink-for-non-root-process Sorry that thread is kinda convoluted. Could you please provide a summary in the commit message and explain why this isn't an issue anymore?
________________________________________ From: Christian Brauner <brauner@kernel.org> Sent: Thursday, March 9, 2023 9:09 AM To: Anjali Kulkarni Cc: davem@davemloft.net; edumazet@google.com; kuba@kernel.org; pabeni@redhat.com; zbr@ioremap.net; johannes@sipsolutions.net; ecree.xilinx@gmail.com; leon@kernel.org; keescook@chromium.org; socketcan@hartkopp.net; petrm@nvidia.com; linux-kernel@vger.kernel.org; netdev@vger.kernel.org Subject: Re: [PATCH 4/5] connector/cn_proc: Allow non-root users access On Wed, Mar 08, 2023 at 07:19:52PM -0800, Anjali Kulkarni wrote: > The patch allows non-root users to receive cn proc connector > notifications, as anyone can normally get process start/exit status from > /proc. The reason for not allowing non-root users to receive multicast > messages is long gone, as described in this thread: > https://urldefense.com/v3/__https://linux-kernel.vger.kernel.narkive.com/CpJFcnra/multicast-netlink-for-non-root-process__;!!ACWV5N9M2RV99hQ!NKjh44Qy5cy18bhIbdhHlHeA1w_i-N5u2PdbQPRTobAEUYW8ZiQ8hkOxaojiLWmq3POJ2k4DaD3CtyC9-C3Cnoo$ Sorry that thread is kinda convoluted. Could you please provide a summary in the commit message and explain why this isn't an issue anymore? ANJALI> Looking into this some more, I think that instead of adding non-root access for all NETLINK_CONNECTOR users by including the flag NL_CFG_F_NONROOT_RECV, we could make this change at an even more fine grained level than protocol level. So I will add a check to enable non-root access only for event notification (cn_proc) user of NETLINK_CONNECTOR, based on the multicast group. Since CONNECTOR is very generic and could be used for varied purposes, a more fine grained approach may be required here. I will send the next patch series with this change.
________________________________________ From: Christian Brauner <brauner@kernel.org> Sent: Thursday, March 9, 2023 9:09 AM To: Anjali Kulkarni Cc: davem@davemloft.net; edumazet@google.com; kuba@kernel.org; pabeni@redhat.com; zbr@ioremap.net; johannes@sipsolutions.net; ecree.xilinx@gmail.com; leon@kernel.org; keescook@chromium.org; socketcan@hartkopp.net; petrm@nvidia.com; linux-kernel@vger.kernel.org; netdev@vger.kernel.org Subject: Re: [PATCH 4/5] connector/cn_proc: Allow non-root users access On Wed, Mar 08, 2023 at 07:19:52PM -0800, Anjali Kulkarni wrote: > The patch allows non-root users to receive cn proc connector > notifications, as anyone can normally get process start/exit status from > /proc. The reason for not allowing non-root users to receive multicast > messages is long gone, as described in this thread: > https://urldefense.com/v3/__https://linux-kernel.vger.kernel.narkive.com/CpJFcnra/multicast-netlink-for-non-root-process__;!!ACWV5N9M2RV99hQ!NKjh44Qy5cy18bhIbdhHlHeA1w_i-N5u2PdbQPRTobAEUYW8ZiQ8hkOxaojiLWmq3POJ2k4DaD3CtyC9-C3Cnoo$ Sorry that thread is kinda convoluted. Could you please provide a summary in the commit message and explain why this isn't an issue anymore? ANJALI> Will change commit message as follows: There were a couple of reasons for not allowing non-root users access initially - one is there was "that at some point there was no proper receive buffer management in place for netlink multicast. But that should be long fixed." according to Andi Kleen & Alexey. Second is that some of the messages may contain data that is root only. But this should be handled with a finer granularity, which is being done at the protocol layer. The only problematic protocols are nf_queue and the firewall netlink, according to Andi. Hence, this restriction for non-root access was relaxed for rtnetlink initially (and subsequently for other protocols as well): https://lore.kernel.org/all/20020612013101.A22399@wotan.suse.de/ Since process connector messages are not sensitive (process fork, exit notifications etc.), and anyone can read /proc data, we can allow non-root access here too. Reason we need this change is we cannot run our DB application as root.
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