On Thu, Apr 13, 2023 at 03:33:52PM +0200, 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@xxxxxxxxxxxxx> > Cc: Eric Dumazet <edumazet@xxxxxxxxxx> > Cc: Jakub Kicinski <kuba@xxxxxxxxxx> > Cc: Paolo Abeni <pabeni@xxxxxxxxxx> > Cc: Leon Romanovsky <leon@xxxxxxxxxx> > Cc: David Ahern <dsahern@xxxxxxxxxx> > Cc: Arnd Bergmann <arnd@xxxxxxxx> > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > Cc: Christian Brauner <brauner@xxxxxxxxxx> > Cc: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> > Cc: Lennart Poettering <mzxreary@xxxxxxxxxxx> > Cc: Luca Boccassi <bluca@xxxxxxxxxx> > Cc: linux-kernel@xxxxxxxxxxxxxxx > Cc: netdev@xxxxxxxxxxxxxxx > Cc: linux-arch@xxxxxxxxxxxxxxx > Tested-by: Luca Boccassi <bluca@xxxxxxxxxx> > Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx> > --- > v4: > - fixed silent fd_install if writting of CMSG to the userspace fails (pointed by Christian) > 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 | 39 +++++++++++++++++++++++-- > 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, 76 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..c67f765a165b 100644 > --- a/include/net/scm.h > +++ b/include/net/scm.h > @@ -120,12 +120,44 @@ static inline bool scm_has_secdata(struct socket *sock) > } > #endif /* CONFIG_SECURITY_NETWORK */ > > +static __inline__ void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm) > +{ > + struct file *pidfd_file = NULL; > + int pidfd; > + > + /* > + * put_cmsg() doesn't return an error if CMSG is truncated, > + * that's why we need to opencode these checks here. > + */ > + if ((msg->msg_controllen <= sizeof(struct cmsghdr)) || > + (msg->msg_controllen - sizeof(struct cmsghdr)) < sizeof(int)) { > + msg->msg_flags |= MSG_CTRUNC; > + return; Hm, curious about this: We mark the message as truncated for SCM_PIDFD but if the same conditions were to apply for SCM_PASSCRED we don't mark the message as truncated. Am I reading this correct? And is so, you please briefly explain this difference? > + } > + > + WARN_ON_ONCE(!scm->pid); > + pidfd = pidfd_prepare(scm->pid, 0, &pidfd_file); > + > + if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) { If the put_cmsg() of the pidfd fails userspace needs to be able to detect this. Otherwise they can't distinguish between the SCM_PIDFD value being zero because the put_cmsg() failed or put_cmsg() succeeded and the allocated fd nr was 0. Looking at put_cmsg() it looks to me that userspace will receive a SCM_PIDFD message only if the put_cmsg() is completely successful. IIUC, then this change is fine.
