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genetlink: Use internal flags for multicast groups 

As explained in commit e03781879a ("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 44ec98ea5e ("psample: Require
'CAP_NET_ADMIN' when joining "packets" group") and commit e03781879a
("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>
This commit is contained in:
Ido Schimmel 2023-12-20 17:43:58 +02:00 committed by David S. Miller
parent f732ba4ac9
commit cd4d7263d5
5 changed files with 11 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
include/net/genetlink.h
View File

@ -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_split_ops;

2
net/core/drop_monitor.c
View File

@ -183,7 +183,7 @@ out:
}
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)

2
net/mptcp/pm_netlink.c
View File

@ -1100,7 +1100,7 @@ int mptcp_pm_nl_get_local_id(struct mptcp_sock *msk, struct mptcp_addr_info *skc
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,
},
};

4
net/netlink/genetlink.c
View File

@ -1829,10 +1829,10 @@ 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;

2
net/psample/psample.c
View File

@ -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;