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syscallcompat: MknodatUser: work around changed syscall.Setgroups semantics 

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.

We now use unix.{Setgroups,Setregid,Setreuid} instead.

Workarounds https://github.com/golang/go/issues/1435 .
This commit is contained in:
Jakob Unterwurzacher 2021-02-06 11:13:22 +01:00
parent 3ab1bcf1c5
commit 80a651a194
2 changed files with 51 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

70
internal/syscallcompat/sys_linux.go
View File

@ -92,28 +92,38 @@ func getSupplementaryGroups(pid uint32) (gids []int) {
}
// OpenatUser runs the Openat syscall in the context of a different user.
//
// It switches the current thread to the new user, performs the syscall,
// and switches back.
func OpenatUser(dirfd int, path string, flags int, mode uint32, context *fuse.Context) (fd int, err error) {
if context != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = syscall.Setgroups(getSupplementaryGroups(context.Pid))
if err != nil {
return -1, err
}
defer syscall.Setgroups(nil)
// 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.
//
// We now use unix.{Setgroups,Setregid,Setreuid} instead.
err = syscall.Setregid(-1, int(context.Owner.Gid))
err = unix.Setgroups(getSupplementaryGroups(context.Pid))
if err != nil {
return -1, err
}
defer syscall.Setregid(-1, 0)
defer unix.Setgroups(nil)
err = syscall.Setreuid(-1, int(context.Owner.Uid))
err = unix.Setregid(-1, int(context.Owner.Gid))
if err != nil {
return -1, err
}
defer syscall.Setreuid(-1, 0)
defer unix.Setregid(-1, 0)
err = unix.Setreuid(-1, int(context.Owner.Uid))
if err != nil {
return -1, err
}
defer unix.Setreuid(-1, 0)
}
return Openat(dirfd, path, flags, mode)
@ -125,28 +135,30 @@ func Mknodat(dirfd int, path string, mode uint32, dev int) (err error) {
}
// MknodatUser runs the Mknodat syscall in the context of a different user.
//
// See OpenatUser() for how this works.
func MknodatUser(dirfd int, path string, mode uint32, dev int, context *fuse.Context) (err error) {
if context != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = syscall.Setgroups(getSupplementaryGroups(context.Pid))
err = unix.Setgroups(getSupplementaryGroups(context.Pid))
if err != nil {
return err
}
defer syscall.Setgroups(nil)
defer unix.Setgroups(nil)
err = syscall.Setregid(-1, int(context.Owner.Gid))
err = unix.Setregid(-1, int(context.Owner.Gid))
if err != nil {
return err
}
defer syscall.Setregid(-1, 0)
defer unix.Setregid(-1, 0)
err = syscall.Setreuid(-1, int(context.Owner.Uid))
err = unix.Setreuid(-1, int(context.Owner.Uid))
if err != nil {
return err
}
defer syscall.Setreuid(-1, 0)
defer unix.Setreuid(-1, 0)
}
return Mknodat(dirfd, path, mode, dev)
@ -193,56 +205,60 @@ func FchmodatNofollow(dirfd int, path string, mode uint32) (err error) {
}
// SymlinkatUser runs the Symlinkat syscall in the context of a different user.
//
// See OpenatUser() for how this works.
func SymlinkatUser(oldpath string, newdirfd int, newpath string, context *fuse.Context) (err error) {
if context != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = syscall.Setgroups(getSupplementaryGroups(context.Pid))
err = unix.Setgroups(getSupplementaryGroups(context.Pid))
if err != nil {
return err
}
defer syscall.Setgroups(nil)
defer unix.Setgroups(nil)
err = syscall.Setregid(-1, int(context.Owner.Gid))
err = unix.Setregid(-1, int(context.Owner.Gid))
if err != nil {
return err
}
defer syscall.Setregid(-1, 0)
defer unix.Setregid(-1, 0)
err = syscall.Setreuid(-1, int(context.Owner.Uid))
err = unix.Setreuid(-1, int(context.Owner.Uid))
if err != nil {
return err
}
defer syscall.Setreuid(-1, 0)
defer unix.Setreuid(-1, 0)
}
return Symlinkat(oldpath, newdirfd, newpath)
}
// MkdiratUser runs the Mkdirat syscall in the context of a different user.
//
// See OpenatUser() for how this works.
func MkdiratUser(dirfd int, path string, mode uint32, caller *fuse.Caller) (err error) {
if caller != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = syscall.Setgroups(getSupplementaryGroups(caller.Pid))
err = unix.Setgroups(getSupplementaryGroups(caller.Pid))
if err != nil {
return err
}
defer syscall.Setgroups(nil)
defer unix.Setgroups(nil)
err = syscall.Setregid(-1, int(caller.Gid))
err = unix.Setregid(-1, int(caller.Gid))
if err != nil {
return err
}
defer syscall.Setregid(-1, 0)
defer unix.Setregid(-1, 0)
err = syscall.Setreuid(-1, int(caller.Uid))
err = unix.Setreuid(-1, int(caller.Uid))
if err != nil {
return err
}
defer syscall.Setreuid(-1, 0)
defer unix.Setreuid(-1, 0)
}
return Mkdirat(dirfd, path, mode)

9
test.bash
View File

@ -80,7 +80,14 @@ else
fi
if grep -R "panic(" ./*.go internal ; then
echo "Please use log.Panic instead of naked panic!"
echo "$MYNAME: Please use log.Panic instead of naked panic!"
exit 1
fi
# All functions from the commit msg in https://go-review.googlesource.com/c/go/+/210639
if grep -R -E 'syscall.(Setegid|Seteuid|Setgroups|Setgid|Setregid|Setreuid|Setresgid|Setresuid|Setuid)\(' \
./*.go internal ; then
echo "$MYNAME: You probably want to use unix.Setgroups and friends. See the comments in OpenatUser() for why."
exit 1
fi