af_unix: rework unix_maybe_add_creds() to allow sleep

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@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kuniyuki Iwashima <kuniyu@google.com>
Cc: Lennart Poettering <mzxreary@0pointer.de>
Cc: Luca Boccassi <bluca@debian.org>
Cc: David Rheinsberg <david@readahead.eu>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Link: https://lore.kernel.org/20250703222314.309967-2-aleksandr.mikhalitsyn@canonical.com
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 129388c309b0d5a4370bb686c31ec7e326eb05c2..fba50ceab42b3c077cecd4a934b022f6b7aebe5b 100644 (file)
--- 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 @@ lookup:
                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 @@ restart_locked:
        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);