tun: use socket locks for sk_{attach,detatch}_filter

This reverts commit 5a5abb1fa3b05dd ("tun, bpf: fix suspicious RCU usage
in tun_{attach, detach}_filter") and replaces it to use lock_sock around
sk_{attach,detach}_filter. The checks inside filter.c are updated with
lockdep_sock_is_held to check for proper socket locks.

It keeps the code cleaner by ensuring that only one lock governs the
socket filter instead of two independent locks.

Cc: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -622,8 +622,9 @@ static int tun_attach(struct tun_struct *tun, struct file *file, bool skip_filte
 
 	/* Re-attach the filter to persist device */
 	if (!skip_filter && (tun->filter_attached == true)) {
-		err = __sk_attach_filter(&tun->fprog, tfile->socket.sk,
-					 lockdep_rtnl_is_held());
+		lock_sock(tfile->socket.sk);
+		err = sk_attach_filter(&tun->fprog, tfile->socket.sk);
+		release_sock(tfile->socket.sk);
 		if (!err)
 			goto out;
 	}
@@ -1824,7 +1825,9 @@ static void tun_detach_filter(struct tun_struct *tun, int n)
 
 	for (i = 0; i < n; i++) {
 		tfile = rtnl_dereference(tun->tfiles[i]);
-		__sk_detach_filter(tfile->socket.sk, lockdep_rtnl_is_held());
+		lock_sock(tfile->socket.sk);
+		sk_detach_filter(tfile->socket.sk);
+		release_sock(tfile->socket.sk);
 	}
 
 	tun->filter_attached = false;
@@ -1837,8 +1840,9 @@ static int tun_attach_filter(struct tun_struct *tun)
 
 	for (i = 0; i < tun->numqueues; i++) {
 		tfile = rtnl_dereference(tun->tfiles[i]);
-		ret = __sk_attach_filter(&tun->fprog, tfile->socket.sk,
-					 lockdep_rtnl_is_held());
+		lock_sock(tfile->socket.sk);
+		ret = sk_attach_filter(&tun->fprog, tfile->socket.sk);
+		release_sock(tfile->socket.sk);
 		if (ret) {
 			tun_detach_filter(tun, i);
 			return ret;

include/linux/filter.h

@@ -465,14 +465,10 @@ int bpf_prog_create_from_user(struct bpf_prog **pfp, struct sock_fprog *fprog,
 void bpf_prog_destroy(struct bpf_prog *fp);
 
 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk);
-int __sk_attach_filter(struct sock_fprog *fprog, struct sock *sk,
-		       bool locked);
 int sk_attach_bpf(u32 ufd, struct sock *sk);
 int sk_reuseport_attach_filter(struct sock_fprog *fprog, struct sock *sk);
 int sk_reuseport_attach_bpf(u32 ufd, struct sock *sk);
 int sk_detach_filter(struct sock *sk);
-int __sk_detach_filter(struct sock *sk, bool locked);
-
 int sk_get_filter(struct sock *sk, struct sock_filter __user *filter,
 		  unsigned int len);
 

net/core/filter.c

@@ -1149,8 +1149,7 @@ void bpf_prog_destroy(struct bpf_prog *fp)
 }
 EXPORT_SYMBOL_GPL(bpf_prog_destroy);
 
-static int __sk_attach_prog(struct bpf_prog *prog, struct sock *sk,
-			    bool locked)
+static int __sk_attach_prog(struct bpf_prog *prog, struct sock *sk)
 {
 	struct sk_filter *fp, *old_fp;
 
@@ -1166,8 +1165,10 @@ static int __sk_attach_prog(struct bpf_prog *prog, struct sock *sk,
 		return -ENOMEM;
 	}
 
-	old_fp = rcu_dereference_protected(sk->sk_filter, locked);
+	old_fp = rcu_dereference_protected(sk->sk_filter,
+					   lockdep_sock_is_held(sk));
 	rcu_assign_pointer(sk->sk_filter, fp);
+
 	if (old_fp)
 		sk_filter_uncharge(sk, old_fp);
 
@@ -1246,8 +1247,7 @@ struct bpf_prog *__get_filter(struct sock_fprog *fprog, struct sock *sk)
  * occurs or there is insufficient memory for the filter a negative
  * errno code is returned. On success the return is zero.
  */
-int __sk_attach_filter(struct sock_fprog *fprog, struct sock *sk,
-		       bool locked)
+int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 {
 	struct bpf_prog *prog = __get_filter(fprog, sk);
 	int err;
@@ -1255,7 +1255,7 @@ int __sk_attach_filter(struct sock_fprog *fprog, struct sock *sk,
 	if (IS_ERR(prog))
 		return PTR_ERR(prog);
 
-	err = __sk_attach_prog(prog, sk, locked);
+	err = __sk_attach_prog(prog, sk);
 	if (err < 0) {
 		__bpf_prog_release(prog);
 		return err;
@@ -1263,12 +1263,7 @@ int __sk_attach_filter(struct sock_fprog *fprog, struct sock *sk,
 
 	return 0;
 }
-EXPORT_SYMBOL_GPL(__sk_attach_filter);
-
-int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
-{
-	return __sk_attach_filter(fprog, sk, sock_owned_by_user(sk));
-}
+EXPORT_SYMBOL_GPL(sk_attach_filter);
 
 int sk_reuseport_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 {
@@ -1314,7 +1309,7 @@ int sk_attach_bpf(u32 ufd, struct sock *sk)
 	if (IS_ERR(prog))
 		return PTR_ERR(prog);
 
-	err = __sk_attach_prog(prog, sk, sock_owned_by_user(sk));
+	err = __sk_attach_prog(prog, sk);
 	if (err < 0) {
 		bpf_prog_put(prog);
 		return err;
@@ -2255,7 +2250,7 @@ static int __init register_sk_filter_ops(void)
 }
 late_initcall(register_sk_filter_ops);
 
-int __sk_detach_filter(struct sock *sk, bool locked)
+int sk_detach_filter(struct sock *sk)
 {
 	int ret = -ENOENT;
 	struct sk_filter *filter;
@@ -2263,7 +2258,8 @@ int __sk_detach_filter(struct sock *sk, bool locked)
 	if (sock_flag(sk, SOCK_FILTER_LOCKED))
 		return -EPERM;
 
-	filter = rcu_dereference_protected(sk->sk_filter, locked);
+	filter = rcu_dereference_protected(sk->sk_filter,
+					   lockdep_sock_is_held(sk));
 	if (filter) {
 		RCU_INIT_POINTER(sk->sk_filter, NULL);
 		sk_filter_uncharge(sk, filter);
@@ -2272,12 +2268,7 @@ int __sk_detach_filter(struct sock *sk, bool locked)
 
 	return ret;
 }
-EXPORT_SYMBOL_GPL(__sk_detach_filter);
-
-int sk_detach_filter(struct sock *sk)
-{
-	return __sk_detach_filter(sk, sock_owned_by_user(sk));
-}
+EXPORT_SYMBOL_GPL(sk_detach_filter);
 
 int sk_get_filter(struct sock *sk, struct sock_filter __user *ubuf,
 		  unsigned int len)
@@ -2288,7 +2279,7 @@ int sk_get_filter(struct sock *sk, struct sock_filter __user *ubuf,
 
 	lock_sock(sk);
 	filter = rcu_dereference_protected(sk->sk_filter,
-					   sock_owned_by_user(sk));
+					   lockdep_sock_is_held(sk));
 	if (!filter)
 		goto out;