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package syscallcompat
import (
"fmt"
"io/ioutil"
"runtime"
"strconv"
"strings"
"github.com/hanwen/go-fuse/v2/fuse"
)
// asUser runs `f()` under the effective uid, gid, groups specified
// in `context`.
//
// If `context` is nil, `f()` is executed directly without switching user id.
func asUser(f func() (int, error), context *fuse.Context) (int, error) {
if context == nil {
return f()
}
runtime.LockOSThread()
defer runtime.UnlockOSThread()
// Since go1.16beta1 (commit d1b1145cace8b968307f9311ff611e4bb810710c ,
// https://go-review.googlesource.com/c/go/+/210639 )
// syscall.{Setgroups,Setregid,Setreuid} affects all threads, which
// is exactly what we not want.
//
// And unix.{Setgroups,Setregid,Setreuid} also changed to this behavoir in
// v0.1.0 (commit d0df966e6959f00dc1c74363e537872647352d51 ,
// https://go-review.googlesource.com/c/sys/+/428174 ), so we use
// our own syscall wrappers.
err := Setgroups(getSupplementaryGroups(context.Pid))
if err != nil {
return -1, err
}
defer SetgroupsPanic(nil)
err = Setregid(-1, int(context.Owner.Gid))
if err != nil {
return -1, err
}
defer SetregidPanic(-1, 0)
err = Setreuid(-1, int(context.Owner.Uid))
if err != nil {
return -1, err
}
defer SetreuidPanic(-1, 0)
return f()
}
func getSupplementaryGroups(pid uint32) (gids []int) {
procPath := fmt.Sprintf("/proc/%d/task/%d/status", pid, pid)
blob, err := ioutil.ReadFile(procPath)
if err != nil {
return nil
}
lines := strings.Split(string(blob), "\n")
for _, line := range lines {
if strings.HasPrefix(line, "Groups:") {
f := strings.Fields(line[7:])
gids = make([]int, len(f))
for i := range gids {
val, err := strconv.ParseInt(f[i], 10, 32)
if err != nil {
return nil
}
gids[i] = int(val)
}
return gids
}
}
return nil
}
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