sock_diag: allow to dump bpf filters

This patch allows to dump BPF filters attached to a socket with
SO_ATTACH_FILTER.
Note that we check CAP_SYS_ADMIN before allowing to dump this info.

For now, only AF_PACKET sockets use this feature.
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/sock_diag.h

 #ifndef __SOCK_DIAG_H__
 #define __SOCK_DIAG_H__
 
+#include <linux/user_namespace.h>
 #include <uapi/linux/sock_diag.h>
 
 struct sk_buff;
@@ -22,5 +23,7 @@ int sock_diag_check_cookie(void *sk, __u32 *cookie);
 void sock_diag_save_cookie(void *sk, __u32 *cookie);
 
 int sock_diag_put_meminfo(struct sock *sk, struct sk_buff *skb, int attr);
+int sock_diag_put_filterinfo(struct user_namespace *user_ns, struct sock *sk,
+			     struct sk_buff *skb, int attrtype);
 
 #endif

include/uapi/linux/packet_diag.h

@@ -17,6 +17,7 @@ struct packet_diag_req {
 #define PACKET_SHOW_RING_CFG	0x00000004 /* Rings configuration parameters */
 #define PACKET_SHOW_FANOUT	0x00000008
 #define PACKET_SHOW_MEMINFO	0x00000010
+#define PACKET_SHOW_FILTER	0x00000020
 
 struct packet_diag_msg {
 	__u8	pdiag_family;
@@ -35,6 +36,7 @@ enum {
 	PACKET_DIAG_FANOUT,
 	PACKET_DIAG_UID,
 	PACKET_DIAG_MEMINFO,
+	PACKET_DIAG_FILTER,
 
 	__PACKET_DIAG_MAX,
 };

net/core/sock_diag.c

@@ -49,6 +49,39 @@ int sock_diag_put_meminfo(struct sock *sk, struct sk_buff *skb, int attrtype)
 }
 EXPORT_SYMBOL_GPL(sock_diag_put_meminfo);
 
+int sock_diag_put_filterinfo(struct user_namespace *user_ns, struct sock *sk,
+			     struct sk_buff *skb, int attrtype)
+{
+	struct nlattr *attr;
+	struct sk_filter *filter;
+	unsigned int len;
+	int err = 0;
+
+	if (!ns_capable(user_ns, CAP_NET_ADMIN)) {
+		nla_reserve(skb, attrtype, 0);
+		return 0;
+	}
+
+	rcu_read_lock();
+
+	filter = rcu_dereference(sk->sk_filter);
+	len = filter ? filter->len * sizeof(struct sock_filter) : 0;
+
+	attr = nla_reserve(skb, attrtype, len);
+	if (attr == NULL) {
+		err = -EMSGSIZE;
+		goto out;
+	}
+
+	if (filter)
+		memcpy(nla_data(attr), filter->insns, len);
+
+out:
+	rcu_read_unlock();
+	return err;
+}
+EXPORT_SYMBOL(sock_diag_put_filterinfo);
+
 void sock_diag_register_inet_compat(int (*fn)(struct sk_buff *skb, struct nlmsghdr *nlh))
 {
 	mutex_lock(&sock_diag_table_mutex);

net/packet/diag.c

@@ -170,6 +170,10 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb,
 	    sock_diag_put_meminfo(sk, skb, PACKET_DIAG_MEMINFO))
 		goto out_nlmsg_trim;
 
+	if ((req->pdiag_show & PACKET_SHOW_FILTER) &&
+	    sock_diag_put_filterinfo(user_ns, sk, skb, PACKET_DIAG_FILTER))
+		goto out_nlmsg_trim;
+
 	return nlmsg_end(skb, nlh);
 
 out_nlmsg_trim: