[PATCH 5.15.y 1/2] genetlink: Use internal flags for multicast groups

[Sasha Levin <sashal@kernel.org>]

From: Ido Schimmel <idosch@nvidia.com>

[ Upstream commit cd4d7263d58ab98fd4dee876776e4da6c328faa3 ]

As explained in commit e03781879a0d ("drop_monitor: Require
'CAP_SYS_ADMIN' when joining "events" group"), the "flags" field in the
multicast group structure reuses uAPI flags despite the field not being
exposed to user space. This makes it impossible to extend its use
without adding new uAPI flags, which is inappropriate for internal
kernel checks.

Solve this by adding internal flags (i.e., "GENL_MCAST_*") and convert
the existing users to use them instead of the uAPI flags.

Tested using the reproducers in commit 44ec98ea5ea9 ("psample: Require
'CAP_NET_ADMIN' when joining "packets" group") and commit e03781879a0d
("drop_monitor: Require 'CAP_SYS_ADMIN' when joining "events" group").

No functional changes intended.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: d1ebfce2c1d1 ("smb: client: require net admin for CIFS SWN netlink")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/net/genetlink.h | 9 ++++++---
 net/core/drop_monitor.c | 2 +-
 net/mptcp/pm_netlink.c  | 2 +-
 net/netlink/genetlink.c | 4 ++--
 net/psample/psample.c   | 2 +-
 5 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index 3cfa33a0aa169..58fdf6de2e5ea 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -8,16 +8,19 @@
 
 #define GENLMSG_DEFAULT_SIZE (NLMSG_DEFAULT_SIZE - GENL_HDRLEN)
 
+/* Binding to multicast group requires %CAP_NET_ADMIN */
+#define GENL_MCAST_CAP_NET_ADMIN	BIT(0)
+/* Binding to multicast group requires %CAP_SYS_ADMIN */
+#define GENL_MCAST_CAP_SYS_ADMIN	BIT(1)
+
 /**
  * struct genl_multicast_group - generic netlink multicast group
  * @name: name of the multicast group, names are per-family
- * @flags: GENL_* flags (%GENL_ADMIN_PERM or %GENL_UNS_ADMIN_PERM)
- * @cap_sys_admin: whether %CAP_SYS_ADMIN is required for binding
+ * @flags: GENL_MCAST_* flags
  */
 struct genl_multicast_group {
 	char			name[GENL_NAMSIZ];
 	u8			flags;
-	u8			cap_sys_admin:1;
 };
 
 struct genl_ops;
diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 24ace3f94b56e..ad5d3090f13fe 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -184,7 +184,7 @@ static struct sk_buff *reset_per_cpu_data(struct per_cpu_dm_data *data)
 }
 
 static const struct genl_multicast_group dropmon_mcgrps[] = {
-	{ .name = "events", .cap_sys_admin = 1 },
+	{ .name = "events", .flags = GENL_MCAST_CAP_SYS_ADMIN, },
 };
 
 static void send_dm_alert(struct work_struct *work)
diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 6fb14148a96e0..14b04992525ea 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -1196,7 +1196,7 @@ void mptcp_pm_nl_data_init(struct mptcp_sock *msk)
 static const struct genl_multicast_group mptcp_pm_mcgrps[] = {
 	[MPTCP_PM_CMD_GRP_OFFSET]	= { .name = MPTCP_PM_CMD_GRP_NAME, },
 	[MPTCP_PM_EV_GRP_OFFSET]        = { .name = MPTCP_PM_EV_GRP_NAME,
-					    .flags = GENL_UNS_ADMIN_PERM,
+					    .flags = GENL_MCAST_CAP_NET_ADMIN,
 					  },
 };
 
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 789cdc1dbcdf6..7a568292e0d10 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -1372,10 +1372,10 @@ static int genl_bind(struct net *net, int group)
 			continue;
 
 		grp = &family->mcgrps[i];
-		if ((grp->flags & GENL_UNS_ADMIN_PERM) &&
+		if ((grp->flags & GENL_MCAST_CAP_NET_ADMIN) &&
 		    !ns_capable(net->user_ns, CAP_NET_ADMIN))
 			ret = -EPERM;
-		if (grp->cap_sys_admin &&
+		if ((grp->flags & GENL_MCAST_CAP_SYS_ADMIN) &&
 		    !ns_capable(net->user_ns, CAP_SYS_ADMIN))
 			ret = -EPERM;
 
diff --git a/net/psample/psample.c b/net/psample/psample.c
index 0d9d9936579e0..f93fcebd0cf02 100644
--- a/net/psample/psample.c
+++ b/net/psample/psample.c
@@ -32,7 +32,7 @@ enum psample_nl_multicast_groups {
 static const struct genl_multicast_group psample_nl_mcgrps[] = {
 	[PSAMPLE_NL_MCGRP_CONFIG] = { .name = PSAMPLE_NL_MCGRP_CONFIG_NAME },
 	[PSAMPLE_NL_MCGRP_SAMPLE] = { .name = PSAMPLE_NL_MCGRP_SAMPLE_NAME,
-				      .flags = GENL_UNS_ADMIN_PERM },
+				      .flags = GENL_MCAST_CAP_NET_ADMIN, },
 };
 
 static struct genl_family psample_nl_family __ro_after_init;
-- 
2.53.0