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Message-ID: <20230322154817.c6qasnixow452e6x@wittgenstein>
Date: Wed, 22 Mar 2023 16:48:17 +0100
From: Christian Brauner <brauner@...nel.org>
To: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
Cc: davem@...emloft.net, linux-kernel@...r.kernel.org,
netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Leon Romanovsky <leon@...nel.org>,
David Ahern <dsahern@...nel.org>,
Arnd Bergmann <arnd@...db.de>,
Kees Cook <keescook@...omium.org>,
Kuniyuki Iwashima <kuniyu@...zon.com>,
Lennart Poettering <mzxreary@...inter.de>,
linux-arch@...r.kernel.org
Subject: Re: [PATCH net-next v2 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD
On Tue, Mar 21, 2023 at 07:33:40PM +0100, Alexander Mikhalitsyn wrote:
> Implement SCM_PIDFD, a new type of CMSG type analogical to SCM_CREDENTIALS,
> but it contains pidfd instead of plain pid, which allows programmers not
> to care about PID reuse problem.
>
> Idea comes from UAPI kernel group:
> https://uapi-group.org/kernel-features/
>
> Big thanks to Christian Brauner and Lennart Poettering for productive
> discussions about this.
>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: Leon Romanovsky <leon@...nel.org>
> Cc: David Ahern <dsahern@...nel.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Christian Brauner <brauner@...nel.org>
> Cc: Kuniyuki Iwashima <kuniyu@...zon.com>
> Cc: Lennart Poettering <mzxreary@...inter.de>
> Cc: linux-kernel@...r.kernel.org
> Cc: netdev@...r.kernel.org
> Cc: linux-arch@...r.kernel.org
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
> ---
> v2:
> According to review comments from Kuniyuki Iwashima and Christian Brauner:
> - use pidfd_create(..) retval as a result
> - whitespace change
> ---
> arch/alpha/include/uapi/asm/socket.h | 2 ++
> arch/mips/include/uapi/asm/socket.h | 2 ++
> arch/parisc/include/uapi/asm/socket.h | 2 ++
> arch/sparc/include/uapi/asm/socket.h | 2 ++
> include/linux/net.h | 1 +
> include/linux/socket.h | 1 +
> include/net/scm.h | 14 ++++++++++++--
> include/uapi/asm-generic/socket.h | 2 ++
> net/core/sock.c | 11 +++++++++++
> net/mptcp/sockopt.c | 1 +
> net/unix/af_unix.c | 18 +++++++++++++-----
> tools/include/uapi/asm-generic/socket.h | 2 ++
> 12 files changed, 51 insertions(+), 7 deletions(-)
>
> diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
> index 739891b94136..ff310613ae64 100644
> --- a/arch/alpha/include/uapi/asm/socket.h
> +++ b/arch/alpha/include/uapi/asm/socket.h
> @@ -137,6 +137,8 @@
>
> #define SO_RCVMARK 75
>
> +#define SO_PASSPIDFD 76
> +
> #if !defined(__KERNEL__)
>
> #if __BITS_PER_LONG == 64
> diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
> index 18f3d95ecfec..762dcb80e4ec 100644
> --- a/arch/mips/include/uapi/asm/socket.h
> +++ b/arch/mips/include/uapi/asm/socket.h
> @@ -148,6 +148,8 @@
>
> #define SO_RCVMARK 75
>
> +#define SO_PASSPIDFD 76
> +
> #if !defined(__KERNEL__)
>
> #if __BITS_PER_LONG == 64
> diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
> index f486d3dfb6bb..df16a3e16d64 100644
> --- a/arch/parisc/include/uapi/asm/socket.h
> +++ b/arch/parisc/include/uapi/asm/socket.h
> @@ -129,6 +129,8 @@
>
> #define SO_RCVMARK 0x4049
>
> +#define SO_PASSPIDFD 0x404A
> +
> #if !defined(__KERNEL__)
>
> #if __BITS_PER_LONG == 64
> diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
> index 2fda57a3ea86..6e2847804fea 100644
> --- a/arch/sparc/include/uapi/asm/socket.h
> +++ b/arch/sparc/include/uapi/asm/socket.h
> @@ -130,6 +130,8 @@
>
> #define SO_RCVMARK 0x0054
>
> +#define SO_PASSPIDFD 0x0055
> +
> #if !defined(__KERNEL__)
>
>
> diff --git a/include/linux/net.h b/include/linux/net.h
> index b73ad8e3c212..c234dfbe7a30 100644
> --- a/include/linux/net.h
> +++ b/include/linux/net.h
> @@ -43,6 +43,7 @@ struct net;
> #define SOCK_PASSSEC 4
> #define SOCK_SUPPORT_ZC 5
> #define SOCK_CUSTOM_SOCKOPT 6
> +#define SOCK_PASSPIDFD 7
>
> #ifndef ARCH_HAS_SOCKET_TYPES
> /**
> diff --git a/include/linux/socket.h b/include/linux/socket.h
> index 13c3a237b9c9..6bf90f251910 100644
> --- a/include/linux/socket.h
> +++ b/include/linux/socket.h
> @@ -177,6 +177,7 @@ static inline size_t msg_data_left(struct msghdr *msg)
> #define SCM_RIGHTS 0x01 /* rw: access rights (array of int) */
> #define SCM_CREDENTIALS 0x02 /* rw: struct ucred */
> #define SCM_SECURITY 0x03 /* rw: security label */
> +#define SCM_PIDFD 0x04 /* ro: pidfd (int) */
>
> struct ucred {
> __u32 pid;
> diff --git a/include/net/scm.h b/include/net/scm.h
> index 585adc1346bd..0c717ae9c8db 100644
> --- a/include/net/scm.h
> +++ b/include/net/scm.h
> @@ -124,8 +124,9 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
> struct scm_cookie *scm, int flags)
> {
> if (!msg->msg_control) {
> - if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp ||
> - scm_has_secdata(sock))
> + if (test_bit(SOCK_PASSCRED, &sock->flags) ||
> + test_bit(SOCK_PASSPIDFD, &sock->flags) ||
> + scm->fp || scm_has_secdata(sock))
> msg->msg_flags |= MSG_CTRUNC;
> scm_destroy(scm);
> return;
> @@ -141,6 +142,15 @@ 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)) {
> + int pidfd;
> +
> + WARN_ON_ONCE(!scm->pid);
> + pidfd = pidfd_create(scm->pid, 0);
> +
> + put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd);
So here we need to also make sure that we can't end up in a situation
where the receiver gets an error message and discards the message but
we've snuck an fd into their fdtable. So callers of scm_recv() should be
in a path where the message can't fail anymore and we're about to return
to userspace.
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