[PATCH net-next v2 1/6] af_unix: rework unix_maybe_add_creds() to allow sleep

[Alexander Mikhalitsyn]

As a preparation for the next patches we need to allow sleeping
in unix_maybe_add_creds() and also return err. Currently, we can't do
that as unix_maybe_add_creds() is being called under unix_state_lock().
There is no need for this, really. So let's move call sites of
this helper a bit and do necessary function signature changes.

Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: Simon Horman <horms@xxxxxxxxxx>
Cc: Leon Romanovsky <leon@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Cc: Lennart Poettering <mzxreary@xxxxxxxxxxx>
Cc: Luca Boccassi <bluca@xxxxxxxxxx>
Cc: David Rheinsberg <david@xxxxxxxxxxxx>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx>
---
v2:
	- fixed kdoc for unix_maybe_add_creds() [ thanks to Kuniyuki's review ]
---
 net/unix/af_unix.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 129388c309b0..fba50ceab42b 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1955,21 +1955,30 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
 	return err;
 }
 
-/*
+/**
+ * unix_maybe_add_creds() - Adds current task uid/gid and struct pid to skb if needed.
+ * @skb: skb to attach creds to.
+ * @sk: Sender sock.
+ * @other: Receiver sock.
+ *
  * Some apps rely on write() giving SCM_CREDENTIALS
  * We include credentials if source or destination socket
  * asserted SOCK_PASSCRED.
+ *
+ * Return: On success zero, on error a negative error code is returned.
  */
-static void unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
-				 const struct sock *other)
+static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
+				const struct sock *other)
 {
 	if (UNIXCB(skb).pid)
-		return;
+		return 0;
 
 	if (unix_may_passcred(sk) || unix_may_passcred(other)) {
 		UNIXCB(skb).pid = get_pid(task_tgid(current));
 		current_uid_gid(&UNIXCB(skb).uid, &UNIXCB(skb).gid);
 	}
+
+	return 0;
 }
 
 static bool unix_skb_scm_eq(struct sk_buff *skb,
@@ -2104,6 +2113,10 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
 		goto out_sock_put;
 	}
 
+	err = unix_maybe_add_creds(skb, sk, other);
+	if (err)
+		goto out_sock_put;
+
 restart:
 	sk_locked = 0;
 	unix_state_lock(other);
@@ -2212,7 +2225,6 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
 	if (sock_flag(other, SOCK_RCVTSTAMP))
 		__net_timestamp(skb);
 
-	unix_maybe_add_creds(skb, sk, other);
 	scm_stat_add(other, skb);
 	skb_queue_tail(&other->sk_receive_queue, skb);
 	unix_state_unlock(other);
@@ -2256,6 +2268,10 @@ static int queue_oob(struct sock *sk, struct msghdr *msg, struct sock *other,
 	if (err < 0)
 		goto out;
 
+	err = unix_maybe_add_creds(skb, sk, other);
+	if (err)
+		goto out;
+
 	skb_put(skb, 1);
 	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, 1);
 
@@ -2275,7 +2291,6 @@ static int queue_oob(struct sock *sk, struct msghdr *msg, struct sock *other,
 		goto out_unlock;
 	}
 
-	unix_maybe_add_creds(skb, sk, other);
 	scm_stat_add(other, skb);
 
 	spin_lock(&other->sk_receive_queue.lock);
@@ -2369,6 +2384,10 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 
 		fds_sent = true;
 
+		err = unix_maybe_add_creds(skb, sk, other);
+		if (err)
+			goto out_free;
+
 		if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES)) {
 			skb->ip_summed = CHECKSUM_UNNECESSARY;
 			err = skb_splice_from_iter(skb, &msg->msg_iter, size,
@@ -2399,7 +2418,6 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 			goto out_free;
 		}
 
-		unix_maybe_add_creds(skb, sk, other);
 		scm_stat_add(other, skb);
 		skb_queue_tail(&other->sk_receive_queue, skb);
 		unix_state_unlock(other);
-- 
2.43.0