Add socket_peerpidfd

Supported on Linux since 6.5.

Author: ids1024

src/backend/libc/net/sockopt.rs

@@ -3,7 +3,7 @@
 use super::ext::{in6_addr_new, in_addr_new};
 use crate::backend::c;
 use crate::backend::conv::{borrowed_fd, ret};
-use crate::fd::BorrowedFd;
+use crate::fd::{BorrowedFd, FromRawFd, OwnedFd, RawFd};
 #[cfg(feature = "alloc")]
 #[cfg(any(
     linux_like,
@@ -1060,6 +1060,13 @@ pub(crate) fn socket_peercred(fd: BorrowedFd<'_>) -> io::Result<UCred> {
     getsockopt(fd, c::SOL_SOCKET, c::SO_PEERCRED)
 }
 
+#[cfg(linux_kernel)]
+#[inline]
+pub(crate) fn socket_peerpidfd(fd: BorrowedFd<'_>) -> io::Result<OwnedFd> {
+    let raw = getsockopt::<RawFd>(fd, c::SOL_SOCKET, c::SO_PEERPIDFD)?;
+    Ok(unsafe { OwnedFd::from_raw_fd(raw) })
+}
+
 #[cfg(target_os = "linux")]
 #[inline]
 pub(crate) fn set_xdp_umem_reg(fd: BorrowedFd<'_>, value: XdpUmemReg) -> io::Result<()> {

src/backend/linux_raw/net/sockopt.rs

@@ -7,7 +7,7 @@
 
 use crate::backend::c;
 use crate::backend::conv::{by_mut, c_uint, ret, socklen_t};
-use crate::fd::BorrowedFd;
+use crate::fd::{BorrowedFd, FromRawFd, OwnedFd, RawFd};
 #[cfg(feature = "alloc")]
 use crate::ffi::CStr;
 use crate::io;
@@ -848,6 +848,12 @@ pub(crate) fn socket_peercred(fd: BorrowedFd<'_>) -> io::Result<UCred> {
     getsockopt(fd, c::SOL_SOCKET, linux_raw_sys::net::SO_PEERCRED)
 }
 
+#[inline]
+pub(crate) fn socket_peerpidfd(fd: BorrowedFd<'_>) -> io::Result<OwnedFd> {
+    let raw = getsockopt::<RawFd>(fd, c::SOL_SOCKET, linux_raw_sys::net::SO_PEERPIDFD)?;
+    Ok(unsafe { OwnedFd::from_raw_fd(raw) })
+}
+
 #[cfg(target_os = "linux")]
 #[inline]
 pub(crate) fn set_xdp_umem_reg(fd: BorrowedFd<'_>, value: XdpUmemReg) -> io::Result<()> {

src/net/sockopt.rs

@@ -183,7 +183,7 @@ use crate::{backend, io};
 ))]
 use alloc::string::String;
 use backend::c;
-use backend::fd::AsFd;
+use backend::fd::{AsFd, OwnedFd};
 use core::time::Duration;
 
 /// Timeout identifier for use with [`set_socket_timeout`] and
@@ -1536,6 +1536,15 @@ pub fn socket_peercred<Fd: AsFd>(fd: Fd) -> io::Result<super::UCred> {
     backend::net::sockopt::socket_peercred(fd.as_fd())
 }
 
+///`getsockopt(fd, SOL_SOCKET, SO_PEERPIDFD)`—Get pidfd of Unix domain peer
+///
+/// Added in Linux 6.5.
+#[cfg(linux_kernel)]
+#[doc(alias = "SO_PEERPIDFD")]
+pub fn socket_peerpidfd<Fd: AsFd>(fd: Fd) -> io::Result<OwnedFd> {
+    backend::net::sockopt::socket_peerpidfd(fd.as_fd())
+}
+
 /// `setsockopt(fd, SOL_XDP, XDP_UMEM_REG, value)`
 ///
 /// On kernel versions only supporting v1, the flags are ignored.

tests/event/select.rs

@@ -88,6 +88,7 @@ fn test_select_with_pipes() {
 #[serial] // for `setrlimit` usage
 fn test_select_with_great_fds() {
     use core::cmp::max;
+    use rustix::fd::{FromRawFd as _, OwnedFd};
     use rustix::io::{read, write};
     use rustix::pipe::pipe;
     use rustix::process::{getrlimit, setrlimit, Resource};
@@ -277,6 +278,7 @@ fn test_select_with_sockets() {
 #[test]
 #[serial] // for `setrlimit` usage, and `crate::init`
 fn test_select_with_maxfd_sockets() {
+    use rustix::fd::{FromRawFd as _, OwnedFd};
     use rustix::net::{recv, send, AddressFamily, RecvFlags, SendFlags, SocketType};
     use rustix::process::{getrlimit, setrlimit, Resource};
     use std::net::{IpAddr, Ipv4Addr, SocketAddr};

tests/net/unix_alloc.rs

@@ -677,6 +677,29 @@ fn test_unix_peercred() {
     };
 }
 
+#[cfg(all(feature = "process", feature = "net", linux_kernel))]
+#[test]
+fn test_unix_peerpidfd() {
+    use rustix::net::{sockopt, AddressFamily, SocketFlags, SocketType};
+    use rustix::process::PidfdFlags;
+
+    let (send_sock, _recv_sock) = rustix::net::socketpair(
+        AddressFamily::UNIX,
+        SocketType::STREAM,
+        SocketFlags::CLOEXEC,
+        None,
+    )
+    .unwrap();
+    let pidfd = sockopt::socket_peerpidfd(&send_sock).unwrap();
+    let own_pidfd =
+        rustix::process::pidfd_open(rustix::process::getpid(), PidfdFlags::empty()).unwrap();
+    // Two pidfds refer to the same process iff their `st_ino` values are the same.
+    assert_eq!(
+        rustix::fs::fstat(pidfd).unwrap().st_ino,
+        rustix::fs::fstat(own_pidfd).unwrap().st_ino
+    )
+}
+
 /// Like `test_unix_msg_with_scm_rights`, but with multiple file descriptors
 /// over multiple control messages.
 #[cfg(not(any(target_os = "redox", target_os = "wasi")))]