Commit a9c49cc2 authored by Alexander Mikhalitsyn's avatar Alexander Mikhalitsyn Committed by Jakub Kicinski
Browse files

net: scm: introduce and use scm_recv_unix helper 

Recently, our friends from bluetooth subsystem reported [1] that after
commit 5e2ff670 ("scm: add SO_PASSPIDFD and SCM_PIDFD") scm_recv()
helper become unusable in kernel modules (because it uses unexported
pidfd_prepare() API).

We were aware of this issue and workarounded it in a hard way
by commit 97154bcf ("af_unix: Kconfig: make CONFIG_UNIX bool").

But recently a new functionality was added in the scope of commit
817efd3cad74 ("Bluetooth: hci_sock: Forward credentials to monitor")
and after that bluetooth can't be compiled as a kernel module.

After some discussion in [1] we decided to split scm_recv() into
two helpers, one won't support SCM_PIDFD (used for unix sockets),
and another one will be completely the same as it was before commit
5e2ff670 ("scm: add SO_PASSPIDFD and SCM_PIDFD").

Link: https://lore.kernel.org/lkml/CAJqdLrpFcga4n7wxBhsFqPQiN8PKFVr6U10fKcJ9W7AcZn+o6Q@mail.gmail.com/

 [1]
Fixes: 5e2ff670 ("scm: add SO_PASSPIDFD and SCM_PIDFD")
Signed-off-by: default avatarAlexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230627174314.67688-3-kuniyu@amazon.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 603fc57a

include/net/scm.h

+25 −10
Original line number Diff line number Diff line
@@ -153,7 +153,7 @@ static __inline__ void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm 
		fd_install(pidfd, pidfd_file);

}



static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,

static inline bool __scm_recv_common(struct socket *sock, struct msghdr *msg,

				     struct scm_cookie *scm, int flags)

{

	if (!msg->msg_control) {
@@ -162,7 +162,7 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg, 
		    scm->fp || scm_has_secdata(sock))

			msg->msg_flags |= MSG_CTRUNC;

		scm_destroy(scm);

		return;

		return false;

	}



	if (test_bit(SOCK_PASSCRED, &sock->flags)) {
@@ -175,19 +175,34 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg, 
		put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);

	}



	if (test_bit(SOCK_PASSPIDFD, &sock->flags))

		scm_pidfd_recv(msg, scm);

	scm_passec(sock, msg, scm);



	scm_destroy_cred(scm);

	if (scm->fp)

		scm_detach_fds(msg, scm);



	scm_passec(sock, msg, scm);

	return true;

}



	if (!scm->fp)

static inline void scm_recv(struct socket *sock, struct msghdr *msg,

			    struct scm_cookie *scm, int flags)

{

	if (!__scm_recv_common(sock, msg, scm, flags))

		return;



	scm_detach_fds(msg, scm);

	scm_destroy_cred(scm);

}



static inline void scm_recv_unix(struct socket *sock, struct msghdr *msg,

				 struct scm_cookie *scm, int flags)

{

	if (!__scm_recv_common(sock, msg, scm, flags))

		return;



	if (test_bit(SOCK_PASSPIDFD, &sock->flags))

		scm_pidfd_recv(msg, scm);



	scm_destroy_cred(scm);

}



#endif /* __LINUX_NET_SCM_H */

net/unix/af_unix.c

+2 −2
Original line number Diff line number Diff line
@@ -2427,7 +2427,7 @@ int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size, 
	}

	err = (flags & MSG_TRUNC) ? skb->len - skip : size;



	scm_recv(sock, msg, &scm, flags);

	scm_recv_unix(sock, msg, &scm, flags);



out_free:

	skb_free_datagram(sk, skb);
@@ -2808,7 +2808,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state, 


	mutex_unlock(&u->iolock);

	if (state->msg)

		scm_recv(sock, state->msg, &scm, flags);

		scm_recv_unix(sock, state->msg, &scm, flags);

	else

		scm_destroy(&scm);

out: