bastion 0.54.0

client-go/mcpconfig_open_linux.go

@@ -0,0 +1,42 @@
+//go:build linux
+
+package main
+
+import (
+	"os"
+	"strconv"
+
+	"golang.org/x/sys/unix"
+)
+
+// mcpOpenRegular opens path for reading only if what it names, after any
+// symlinks, is a regular file, without ever opening anything else. The first
+// open is O_PATH: it resolves the path and pins the inode but does not open
+// the file (no driver runs, a FIFO does not wait). Only once fstat says
+// regular is that same inode reopened for reading through /proc/self/fd, so
+// swapping the path between the look and the read reaches nothing new.
+func mcpOpenRegular(path string) (*os.File, string, error) {
+	pfd, err := unix.Open(path, unix.O_PATH|unix.O_CLOEXEC, 0)
+	if err != nil {
+		return nil, "", &os.PathError{Op: "open", Path: path, Err: err}
+	}
+	defer unix.Close(pfd)
+	var st unix.Stat_t
+	if err := unix.Fstat(pfd, &st); err != nil {
+		return nil, "", &os.PathError{Op: "fstat", Path: path, Err: err}
+	}
+	if st.Mode&unix.S_IFMT != unix.S_IFREG {
+		return nil, "", errMCPNotRegular
+	}
+	fd, err := unix.Open("/proc/self/fd/"+strconv.Itoa(pfd), unix.O_RDONLY|unix.O_CLOEXEC|unix.O_NOCTTY|unix.O_NONBLOCK, 0)
+	if err != nil {
+		return nil, "", &os.PathError{Op: "reopen", Path: path, Err: err}
+	}
+	f := os.NewFile(uintptr(fd), path)
+	fi, err := f.Stat()
+	if err != nil || !fi.Mode().IsRegular() {
+		f.Close()
+		return nil, "", errMCPNotRegular
+	}
+	return f, mcpFileOwner(fi), nil
+}