helper/bwrap: integrate seccomp into helper interface

This makes API usage much cleaner, and encapsulates all bwrap arguments in argsWt.

Signed-off-by: Ophestra <cat@gensokyo.uk>

helper/bwrap/seccomp-resolve.go

@@ -0,0 +1,95 @@
+package bwrap
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	"git.gensokyo.uk/security/fortify/internal/fmsg"
+)
+
+type SyscallPolicy struct {
+	DenyDevel bool `json:"deny_devel"`
+	Multiarch bool `json:"multiarch"`
+	Linux32   bool `json:"linux32"`
+	Can       bool `json:"can"`
+	Bluetooth bool `json:"bluetooth"`
+}
+
+type seccompBuilder struct {
+	config *Config
+}
+
+func (s *seccompBuilder) Len() int {
+	if s == nil {
+		return 0
+	}
+	return 2
+}
+
+func (s *seccompBuilder) Append(args *[]string, extraFiles *[]*os.File) error {
+	if s == nil {
+		return nil
+	}
+	if f, err := s.config.resolveSeccomp(); err != nil {
+		return err
+	} else {
+		extraFile(args, extraFiles, positionalArgs[Seccomp], f)
+		return nil
+	}
+}
+
+func (c *Config) resolveSeccomp() (*os.File, error) {
+	if c.Syscall == nil {
+		return nil, nil
+	}
+
+	// resolve seccomp filter opts
+	var (
+		opts    syscallOpts
+		optd    []string
+		optCond = [...]struct {
+			v bool
+			o syscallOpts
+			d string
+		}{
+			{!c.UserNS, flagDenyNS, "denyns"},
+			{c.NewSession, flagDenyTTY, "denytty"},
+			{c.Syscall.DenyDevel, flagDenyDevel, "denydevel"},
+			{c.Syscall.Multiarch, flagMultiarch, "multiarch"},
+			{c.Syscall.Linux32, flagLinux32, "linux32"},
+			{c.Syscall.Can, flagCan, "can"},
+			{c.Syscall.Bluetooth, flagBluetooth, "bluetooth"},
+		}
+	)
+	if CPrintln != nil {
+		optd = make([]string, 1, len(optCond)+1)
+		optd[0] = "common"
+	}
+	for _, opt := range optCond {
+		if opt.v {
+			opts |= opt.o
+			if fmsg.Verbose() {
+				optd = append(optd, opt.d)
+			}
+		}
+	}
+	if CPrintln != nil {
+		CPrintln(fmt.Sprintf("seccomp flags: %s", optd))
+	}
+
+	// export seccomp filter to tmpfile
+	if f, err := tmpfile(); err != nil {
+		return nil, err
+	} else {
+		return f, exportAndSeek(f, opts)
+	}
+}
+
+func exportAndSeek(f *os.File, opts syscallOpts) error {
+	if err := exportFilter(f.Fd(), opts); err != nil {
+		return err
+	}
+	_, err := f.Seek(0, io.SeekStart)
+	return err
+}