internal: add wrappers for securejoin.Proc*

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

Author: cyphar

internal/pathrs/procfs_pathrslite.go

@@ -19,11 +19,83 @@
 package pathrs
 
 import (
+	"fmt"
 	"os"
 
 	"github.com/cyphar/filepath-securejoin/pathrs-lite"
+	"github.com/cyphar/filepath-securejoin/pathrs-lite/procfs"
 )
 
+func procOpenReopen(openFn func(subpath string) (*os.File, error), subpath string, flags int) (*os.File, error) {
+	handle, err := openFn(subpath)
+	if err != nil {
+		return nil, err
+	}
+	defer handle.Close()
+
+	f, err := pathrs.Reopen(handle, flags)
+	if err != nil {
+		return nil, fmt.Errorf("reopen %s: %w", handle.Name(), err)
+	}
+	return f, nil
+}
+
+// ProcSelfOpen is a wrapper around [procfs.Handle.OpenSelf] and
+// [pathrs.Reopen], to let you one-shot open a procfs file with the given
+// flags.
+func ProcSelfOpen(subpath string, flags int) (*os.File, error) {
+	proc, err := procfs.OpenProcRoot()
+	if err != nil {
+		return nil, err
+	}
+	defer proc.Close()
+	return procOpenReopen(proc.OpenSelf, subpath, flags)
+}
+
+// ProcPidOpen is a wrapper around [procfs.Handle.OpenPid] and [pathrs.Reopen],
+// to let you one-shot open a procfs file with the given flags.
+func ProcPidOpen(pid int, subpath string, flags int) (*os.File, error) {
+	proc, err := procfs.OpenProcRoot()
+	if err != nil {
+		return nil, err
+	}
+	defer proc.Close()
+	return procOpenReopen(func(subpath string) (*os.File, error) {
+		return proc.OpenPid(pid, subpath)
+	}, subpath, flags)
+}
+
+// ProcThreadSelfOpen is a wrapper around [procfs.Handle.OpenThreadSelf] and
+// [pathrs.Reopen], to let you one-shot open a procfs file with the given
+// flags. The returned [procfs.ProcThreadSelfCloser] needs the same handling as
+// when using pathrs-lite.
+func ProcThreadSelfOpen(subpath string, flags int) (_ *os.File, _ procfs.ProcThreadSelfCloser, Err error) {
+	proc, err := procfs.OpenProcRoot()
+	if err != nil {
+		return nil, nil, err
+	}
+	defer proc.Close()
+
+	handle, closer, err := proc.OpenThreadSelf(subpath)
+	if err != nil {
+		return nil, nil, err
+	}
+	if closer != nil {
+		defer func() {
+			if Err != nil {
+				closer()
+			}
+		}()
+	}
+	defer handle.Close()
+
+	f, err := pathrs.Reopen(handle, flags)
+	if err != nil {
+		return nil, nil, fmt.Errorf("reopen %s: %w", handle.Name(), err)
+	}
+	return f, closer, nil
+}
+
 // Reopen is a wrapper around pathrs.Reopen.
 func Reopen(file *os.File, flags int) (*os.File, error) {
 	return pathrs.Reopen(file, flags)