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net: scm: introduce and use scm_recv_unix helper

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Recently, our friends from bluetooth subsystem reported [1] that after
commit 5e2ff6704a ("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 97154bcf4d ("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
5e2ff6704a ("scm: add SO_PASSPIDFD and SCM_PIDFD").

Link: https://lore.kernel.org/lkml/CAJqdLrpFcga4n7wxBhsFqPQiN8PKFVr6U10fKcJ9W7AcZn+o6Q@mail.gmail.com/ [1]
Fixes: 5e2ff6704a ("scm: add SO_PASSPIDFD and SCM_PIDFD")
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230627174314.67688-3-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Alexander Mikhalitsyn 2023-06-27 10:43:14 -07:00 committed by Jakub Kicinski
parent 603fc57ab7
commit a9c49cc2f5
2 changed files with 28 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
include/net/scm.h
View File

@ -153,8 +153,8 @@ 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) ||
@ -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);
}
scm_passec(sock, msg, scm);
if (scm->fp)
scm_detach_fds(msg, scm);
return true;
}
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_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);
scm_passec(sock, msg, scm);
if (!scm->fp)
return;
scm_detach_fds(msg, scm);
}
#endif /* __LINUX_NET_SCM_H */

4
net/unix/af_unix.c
View File

@ -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 @@ unlock:
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: