fortify/internal/app/share.system.go
Ophestra Umiker af15b1c048
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app: support mapping target uid as privileged uid in sandbox
Chromium's D-Bus client implementation refuses to work when its getuid call returns a different value than what the D-Bus server is running as. The reason behind this is not fully understood, but this workaround is implemented to support chromium and electron apps. This is not used by default since it has many side effects that break many other programs, like SSH on NixOS.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>
2024-11-04 03:15:39 +09:00

72 lines
2.3 KiB
Go

package app
import (
"path"
"git.ophivana.moe/security/fortify/acl"
"git.ophivana.moe/security/fortify/internal/linux"
"git.ophivana.moe/security/fortify/internal/system"
)
const (
shell = "SHELL"
)
// shareSystem queues various system-related actions
func (seal *appSeal) shareSystem() {
// ensure Share (e.g. `/tmp/fortify.%d`)
// acl is unnecessary as this directory is world executable
seal.sys.Ensure(seal.SharePath, 0701)
// ensure process-specific share (e.g. `/tmp/fortify.%d/%s`)
// acl is unnecessary as this directory is world executable
seal.share = path.Join(seal.SharePath, seal.id)
seal.sys.Ephemeral(system.Process, seal.share, 0701)
// ensure child tmpdir parent directory (e.g. `/tmp/fortify.%d/tmpdir`)
targetTmpdirParent := path.Join(seal.SharePath, "tmpdir")
seal.sys.Ensure(targetTmpdirParent, 0700)
seal.sys.UpdatePermType(system.User, targetTmpdirParent, acl.Execute)
// ensure child tmpdir (e.g. `/tmp/fortify.%d/tmpdir/%d`)
targetTmpdir := path.Join(targetTmpdirParent, seal.sys.user.Uid)
seal.sys.Ensure(targetTmpdir, 01700)
seal.sys.UpdatePermType(system.User, targetTmpdir, acl.Read, acl.Write, acl.Execute)
seal.sys.bwrap.Bind(targetTmpdir, "/tmp", false, true)
// mount tmpfs on inner shared directory (e.g. `/tmp/fortify.%d`)
seal.sys.bwrap.Tmpfs(seal.SharePath, 1*1024*1024)
}
func (seal *appSeal) sharePasswd(os linux.System) {
// look up shell
sh := "/bin/sh"
if s, ok := os.LookupEnv(shell); ok {
seal.sys.bwrap.SetEnv[shell] = s
sh = s
}
// generate /etc/passwd
passwdPath := path.Join(seal.share, "passwd")
username := "chronos"
if seal.sys.user.Username != "" {
username = seal.sys.user.Username
seal.sys.bwrap.SetEnv["USER"] = seal.sys.user.Username
}
homeDir := "/var/empty"
if seal.sys.user.HomeDir != "" {
homeDir = seal.sys.user.HomeDir
seal.sys.bwrap.SetEnv["HOME"] = seal.sys.user.HomeDir
}
passwd := username + ":x:" + seal.sys.mappedIDString + ":" + seal.sys.mappedIDString + ":Fortify:" + homeDir + ":" + sh + "\n"
seal.sys.Write(passwdPath, passwd)
// write /etc/group
groupPath := path.Join(seal.share, "group")
seal.sys.Write(groupPath, "fortify:x:"+seal.sys.mappedIDString+":\n")
// bind /etc/passwd and /etc/group
seal.sys.bwrap.Bind(passwdPath, "/etc/passwd")
seal.sys.bwrap.Bind(groupPath, "/etc/group")
}