Have the netlink per-protocol optional bind function return an int error code
rather than void to signal a failure.
This will enable netlink protocols to perform extra checks including
capabilities and permissions verifications when updating memberships in
multicast groups.
In netlink_bind() and netlink_setsockopt() the call to the per-protocol bind
function was moved above the multicast group update to prevent any access to
the multicast socket groups before checking with the per-protocol bind
function. This will enable the per-protocol bind function to be used to check
permissions which could be denied before making them available, and to avoid
the messy job of undoing the addition should the per-protocol bind function
fail.
The netfilter subsystem seems to be the only one currently using the
per-protocol bind function.
Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
---
In particular, the audit subsystem (NETLINK_AUDIT protocol) could benefit by
being able to check specific capabilities for each multicast group before
granting membership to the requesting socket. Currently, all NETLINK_AUDIT
sockets must have the capability CAP_NET_ADMIN. No other capabilities are
required to join a multicast group. This capability is too broad allowing
access to this socket by many applications that must not have access to this
information. It is proposed to add capability CAP_AUDIT_READ to allow this
access while dropping the exessively broad capability CAP_NET_ADMIN.
There has also been some interest expressed by IETF ForCES folk.
---
include/linux/netlink.h | 2 +-
net/netfilter/nfnetlink.c | 3 ++-
net/netlink/af_netlink.c | 30 +++++++++++++++++-------------
net/netlink/af_netlink.h | 4 ++--
4 files changed, 22 insertions(+), 17 deletions(-)
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 7a6c396..4402653 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -45,7 +45,7 @@ struct netlink_kernel_cfg {
unsigned int flags;
void (*input)(struct sk_buff *skb);
struct mutex *cb_mutex;
- void (*bind)(int group);
+ int (*bind)(int group);
bool (*compare)(struct net *net, struct sock *sk);
};
diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 75619f9..10a4cf5 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -392,7 +392,7 @@ static void nfnetlink_rcv(struct sk_buff *skb)
}
#ifdef CONFIG_MODULES
-static void nfnetlink_bind(int group)
+static int nfnetlink_bind(int group)
{
const struct nfnetlink_subsystem *ss;
int type = nfnl_group2type[group];
@@ -403,6 +403,7 @@ static void nfnetlink_bind(int group)
if (!ss) {
request_module("nfnetlink-subsys-%d", type);
}
+ return 0;
}
#endif
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index bca50b9..4224dc5 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1198,7 +1198,7 @@ static int netlink_create(struct net *net, struct socket *sock, int protocol,
struct module *module = NULL;
struct mutex *cb_mutex;
struct netlink_sock *nlk;
- void (*bind)(int group);
+ int (*bind)(int group);
int err = 0;
sock->state = SS_UNCONNECTED;
@@ -1441,6 +1441,17 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
if (!nladdr->nl_groups && (nlk->groups == NULL || !(u32)nlk->groups[0]))
return 0;
+ if (nlk->netlink_bind && nladdr->nl_groups) {
+ int i;
+
+ for (i = 0; i < nlk->ngroups; i++)
+ if (test_bit(i, (long unsigned int *)&nladdr->nl_groups)) {
+ err = nlk->netlink_bind(i);
+ if (err)
+ return err;
+ }
+ }
+
netlink_table_grab();
netlink_update_subscriptions(sk, nlk->subscriptions +
hweight32(nladdr->nl_groups) -
@@ -1449,15 +1460,6 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
netlink_update_listeners(sk);
netlink_table_ungrab();
- if (nlk->netlink_bind && nlk->groups[0]) {
- int i;
-
- for (i=0; i<nlk->ngroups; i++) {
- if (test_bit(i, nlk->groups))
- nlk->netlink_bind(i);
- }
- }
-
return 0;
}
@@ -2095,14 +2097,16 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
return err;
if (!val || val - 1 >= nlk->ngroups)
return -EINVAL;
+ if (nlk->netlink_bind) {
+ err = nlk->netlink_bind(val);
+ if (err)
+ return err;
+ }
netlink_table_grab();
netlink_update_socket_mc(nlk, val,
optname == NETLINK_ADD_MEMBERSHIP);
netlink_table_ungrab();
- if (nlk->netlink_bind)
- nlk->netlink_bind(val);
-
err = 0;
break;
}
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index acbd774..0edb8d5 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -37,7 +37,7 @@ struct netlink_sock {
struct mutex *cb_mutex;
struct mutex cb_def_mutex;
void (*netlink_rcv)(struct sk_buff *skb);
- void (*netlink_bind)(int group);
+ int (*netlink_bind)(int group);
struct module *module;
#ifdef CONFIG_NETLINK_MMAP
struct mutex pg_vec_lock;
@@ -73,7 +73,7 @@ struct netlink_table {
unsigned int groups;
struct mutex *cb_mutex;
struct module *module;
- void (*bind)(int group);
+ int (*bind)(int group);
bool (*compare)(struct net *net, struct sock *sock);
int registered;
};
--
1.7.1
--
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