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Subject[PATCH][v6] netlink: have netlink per-protocol bind function return an error code.
Date
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@redhat.com>
---
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.

v6: *really* fixed a logic error (missing braces) and a C99 error.

v3: added netlink_unbind() option and unwound netlink_insert().
---
include/linux/netlink.h | 3 ++-
net/netfilter/nfnetlink.c | 3 ++-
net/netlink/af_netlink.c | 41 ++++++++++++++++++++++++++++-------------
net/netlink/af_netlink.h | 6 ++++--
4 files changed, 36 insertions(+), 17 deletions(-)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 7a6c396..0ba2edd 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -45,7 +45,8 @@ 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);
+ void (*unbind)(int group);
bool (*compare)(struct net *net, struct sock *sk);
};

diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 1da5ef1..14c8ac8 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];
@@ -402,6 +402,7 @@ static void nfnetlink_bind(int group)
rcu_read_unlock();
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..45dccff 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1198,7 +1198,8 @@ 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);
+ void (*unbind)(int group);
int err = 0;

sock->state = SS_UNCONNECTED;
@@ -1224,6 +1225,7 @@ static int netlink_create(struct net *net, struct socket *sock, int protocol,
err = -EPROTONOSUPPORT;
cb_mutex = nl_table[protocol].cb_mutex;
bind = nl_table[protocol].bind;
+ unbind = nl_table[protocol].unbind;
netlink_unlock_table();

if (err < 0)
@@ -1240,6 +1242,7 @@ static int netlink_create(struct net *net, struct socket *sock, int protocol,
nlk = nlk_sk(sock->sk);
nlk->module = module;
nlk->netlink_bind = bind;
+ nlk->netlink_unbind = unbind;
out:
return err;

@@ -1293,6 +1296,7 @@ static int netlink_release(struct socket *sock)
kfree_rcu(old, rcu);
nl_table[sk->sk_protocol].module = NULL;
nl_table[sk->sk_protocol].bind = NULL;
+ nl_table[sk->sk_protocol].unbind = NULL;
nl_table[sk->sk_protocol].flags = 0;
nl_table[sk->sk_protocol].registered = 0;
}
@@ -1441,6 +1445,24 @@ 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) {
+ int undo;
+ if (!nlk->portid)
+ netlink_remove(sk);
+ for (undo = 0; undo < i; undo++)
+ if (nlk->netlink_unbind)
+ nlk->netlink_unbind(undo);
+ return err;
+ }
+ }
+ }
+
netlink_table_grab();
netlink_update_subscriptions(sk, nlk->subscriptions +
hweight32(nladdr->nl_groups) -
@@ -1449,15 +1471,6 @@ 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 +2108,16 @@ 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..2aeae8a 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -37,7 +37,8 @@ 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);
+ void (*netlink_unbind)(int group);
struct module *module;
#ifdef CONFIG_NETLINK_MMAP
struct mutex pg_vec_lock;
@@ -73,7 +74,8 @@ struct netlink_table {
unsigned int groups;
struct mutex *cb_mutex;
struct module *module;
- void (*bind)(int group);
+ int (*bind)(int group);
+ void (*unbind)(int group);
bool (*compare)(struct net *net, struct sock *sock);
int registered;
};
--
1.7.1


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