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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Willem de Bruijn CC: Simon Horman , Christian Brauner , Kuniyuki Iwashima , Kuniyuki Iwashima , Subject: [PATCH v1 net-next 5/7] af_unix: Inherit sk_flags at connect(). Date: Wed, 7 May 2025 18:29:17 -0700 Message-ID: <20250508013021.79654-6-kuniyu@amazon.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250508013021.79654-1-kuniyu@amazon.com> References: <20250508013021.79654-1-kuniyu@amazon.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: EX19D039UWB002.ant.amazon.com (10.13.138.79) To EX19D004ANA001.ant.amazon.com (10.37.240.138) For SOCK_STREAM embryo sockets, the SO_PASS{CRED,PIDFD,SEC} options are inherited from the parent listen()ing socket. Currently, this inheritance happens at accept(), because these attributes were stored in sk->sk_socket->flags and the struct socket is not allocated until accept(). This leads to unintentional behaviour. When a peer sends data to an embryo socket in the accept() queue, maybe_add_creds() embeds credentials into the skb, even if neither the peer nor the listener has enabled these options. If the option is enabled, the embryo socket receives the ancillary data after accept(). If not, the data is silently discarded. This conservative approach works for SO_PASS{CRED,PIDFD,SEC}, but not for SO_PASSRIGHTS; once an SCM_RIGHTS with a hung file descriptor is sent, it’s game over. To avoid this, we will need to preserve SOCK_PASSRIGHTS even on embryo sockets. A recent change made it possible to access the parent's flags in sendmsg() via unix_sk(other)->listener->sk->sk_socket->flags, but this introduces an unnecessary condition that is irrelevant for most sockets (i.e., accepted sockets and clients). Therefore, we moved SOCK_PASSXXX into sk->sk_flags, which does not depend on struct socket. Let’s inherit sk->sk_flags at connect() to avoid receiving SCM_RIGHTS on embryo sockets created from a parent with SO_PASSRIGHTS=0. While at it, whitespace issues around pid assignment have been fixed. Signed-off-by: Kuniyuki Iwashima --- net/unix/af_unix.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index e793e55f6c9b..daa7a8ead243 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1631,6 +1631,7 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr, newsk->sk_state = TCP_ESTABLISHED; newsk->sk_type = sk->sk_type; init_peercred(newsk); + sock_copy_flags(newsk, other); newu = unix_sk(newsk); newu->listener = other; RCU_INIT_POINTER(newsk->sk_wq, &newu->peer_wq); @@ -1747,7 +1748,6 @@ static int unix_accept(struct socket *sock, struct socket *newsock, unix_state_lock(tsk); unix_update_edges(unix_sk(tsk)); newsock->state = SS_CONNECTED; - sock_copy_flags(tsk, sk); sock_graft(tsk, newsock); unix_state_unlock(tsk); return 0; @@ -1856,7 +1856,7 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen { int err = 0; - UNIXCB(skb).pid = get_pid(scm->pid); + UNIXCB(skb).pid = get_pid(scm->pid); UNIXCB(skb).uid = scm->creds.uid; UNIXCB(skb).gid = scm->creds.gid; UNIXCB(skb).fp = NULL; @@ -1879,9 +1879,8 @@ static void maybe_add_creds(struct sk_buff *skb, const struct sock *sk, if (UNIXCB(skb).pid) return; - if (unix_passcred_enabled(sk) || - !other->sk_socket || unix_passcred_enabled(other)) { - UNIXCB(skb).pid = get_pid(task_tgid(current)); + if (unix_passcred_enabled(sk) || unix_passcred_enabled(other)) { + UNIXCB(skb).pid = get_pid(task_tgid(current)); current_uid_gid(&UNIXCB(skb).uid, &UNIXCB(skb).gid); } } -- 2.49.0