Recently, our friends from bluetooth subsystem reported
[1] that after ("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 ("af_unix: Kconfig: make CONFIG_UNIX bool").
But recently a new functionality was added in the scope of
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
("scm: add SO_PASSPIDFD and SCM_PIDFD").
[1] https://lore.kernel.org/lkml/CAJqdLrpFcga4n7wxBhsFqPQiN8PKFVr6U10fKcJ9W7AcZn+o6Q@xxxxxxxxxxxxxx/
Cc: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-bluetooth@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
---
include/net/scm.h | 35 +++++++++++++++++++++++++----------
net/unix/af_unix.c | 4 ++--
2 files changed, 27 insertions(+), 12 deletions(-)
diff --git a/include/net/scm.h b/include/net/scm.h
index c67f765a165b..409b8efda2c9 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -151,8 +151,8 @@ 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,
- struct scm_cookie *scm, int flags)
+static inline bool __scm_recv_common(struct socket *sock, struct msghdr *msg,
+ struct scm_cookie *scm, int flags)
{
if (!msg->msg_control) {
if (test_bit(SOCK_PASSCRED, &sock->flags) ||
@@ -160,7 +160,7 @@ 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)) {
@@ -173,19 +173,34 @@ 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 */
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index f2f234f0b92c..20ac83e012e4 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -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 && check_creds)
- scm_recv(sock, state->msg, &scm, flags);
+ scm_recv_unix(sock, state->msg, &scm, flags);
else
scm_destroy(&scm);
out:
--
2.34.1
