pick: Add initial support for libsubid

Pick and adapt apptainer/apptainer#2433

Original description:

This commit adds support for remote access to /etc/subuid and
/etc/subgid mappings from ldap services using libsubid. Requires
shadow-utils + libsubid.

Code ported from podman / container storage.

Signed-off-by: Andrew E. Bruno <[email protected]>

.circleci/config.yml

@@ -99,6 +99,7 @@ commands:
               libfuse-dev \
               libglib2.0-dev \
               libseccomp-dev \
+              libsubid-dev \
               libtool \
               pkg-config \
               squashfs-tools \

.golangci.yml

@@ -5,6 +5,7 @@ run:
     - apparmor
     - e2e_test
     - fakeroot_engine
+    - libsubid
     - seccomp
     - selinux
     - singularity_engine

.vscode/settings.json

@@ -4,7 +4,7 @@
         "--fast"
     ],
     "go.buildFlags": [
-        "-tags=apparmor,fakeroot_engine,seccomp,selinux,singularity_engine,sylog"
+        "-tags=apparmor,fakeroot_engine,libsubid,seccomp,selinux,singularity_engine,sylog"
     ],
     "go.testTags": "apparmor,fakeroot_engine,seccomp,selinux,singularity_engine,sylog,e2e_test,integration_test"
 }

CHANGELOG.md

@@ -7,6 +7,12 @@
 - Use correct username (not user's name) when computing `singularity oci` conmon
   / singularity state dir.
 
+### New Features & Functionality
+
+- Add support for libsubid. Sub[ug]id mappings will be retrieved from e.g. LDAP
+  via libsubid and sssd if Singularity is built with libsubid support (default
+  when libsubid headers are available).
+
 ## 4.2.2 \[2024-12-20\]
 
 ### Bug Fixes

CONTRIBUTORS.md

@@ -22,6 +22,7 @@ The following have contributed code and/or documentation to this repository.
 - Alexander Grund <[email protected]>
 - Amanda Duffy <[email protected]>
 - Ana Guerrero Lopez <[email protected]>
+- Andrew Bruno <[email protected]>
 - Ángel Bejarano <[email protected]>
 - Apuã Paquola <[email protected]>
 - Aron Öfjörð Jóhannesson <[email protected]>

INSTALL.md

@@ -36,6 +36,12 @@ sudo apt-get install -y \
     zlib1g-dev
 ```
 
+To include support for libsubid on Ubuntu 24.04 and above:
+
+```sh
+sudo apt-get install -y libsubid-dev
+```
+
 ### RHEL / Alma Linux / Rocky Linux 8+ and Fedora
 
 ```sh
@@ -59,6 +65,18 @@ sudo yum install -y \
     zlib-devel
 ```
 
+To include support for libsubid:
+
+```sh
+# EL
+sudo dnf --enablerepo=devel install shadow-utils-subid-devel
+
+# Fedora
+sudo dnf install shadow-utils-subid-devel
+```
+
+On SLE/openSUSE
+
 ### SLES / openSUSE Leap
 
 ```sh

LICENSE_THIRD_PARTY.md

@@ -292,6 +292,14 @@ The source files:
 
 Contain code from the podman project, under the Apache License, Version 2.0.
 
+## github.com/containers/storage
+
+The source file:
+
+* `internal/pkg/fakeroot/idtools_supported.go`
+
+Contains code from the podman project, under the Apache License, Version 2.0.
+
 ## github.com/containers/conmon
 
 The source files:

dist/rpm/singularity-ce.spec.in

@@ -88,6 +88,12 @@ Requires: fuse
 # FUSE 3 for squashfuse
 Requires: fuse3
 %endif
+# Libsubid on EL / OpenSuseTumbleweed
+%if "%{_target_vendor}" == "suse" && 0%{?suse_version} > 1600
+BuildRequires: libsubid-devel
+%else
+BuildRequires: shadow-utils-subid-devel
+%endif
 
 Provides: %{name}-runtime
 

internal/pkg/fakeroot/fakeroot.go

@@ -1,4 +1,6 @@
-// Copyright (c) 2019-2021, Sylabs Inc. All rights reserved.
+// Copyright (c) 2019-2025, Sylabs Inc. All rights reserved.
+// Copyright (c) Contributors to the Apptainer project, established as
+//   Apptainer a Series of LF Projects LLC.
 // This software is licensed under a 3-clause BSD license. Please consult the
 // LICENSE.md file distributed with the sources of this project regarding your
 // rights to use or distribute this software.
@@ -300,19 +302,24 @@ func (c *Config) GetUserEntry(username string) (*Entry, error) {
 	if err != nil {
 		return nil, fmt.Errorf("could not retrieve user information for %s: %s", username, err)
 	}
-	for _, entry := range c.entries {
+
+	entries, err := c.getMappingEntries(u)
+	if err != nil {
+		return nil, fmt.Errorf("failed to look up mapping entries for user %s: %w", username, err)
+	}
+
+	for _, entry := range entries {
 		if entry.invalid {
 			continue
 		}
-		if entry.UID == u.UID {
-			if entry.Count == validRangeCount {
-				return entry, nil
-			} else if entry.Count > validRangeCount {
-				largeRangeEntries = append(largeRangeEntries, entry)
-				continue
-			}
-			entryCount++
+
+		if entry.Count == validRangeCount {
+			return entry, nil
+		} else if entry.Count > validRangeCount {
+			largeRangeEntries = append(largeRangeEntries, entry)
+			continue
 		}
+		entryCount++
 	}
 	var largestEntry *Entry
 

internal/pkg/fakeroot/idtools_supported.go

@@ -0,0 +1,123 @@
+//go:build linux && cgo && libsubid
+// +build linux,cgo,libsubid
+
+// Portions of this code was adopted from github.com/containers/storage
+// Copyright (C) The Linux Foundation and its contributors.
+// Original source released under: Apache 2.0 license
+// See: https://github.com/containers/storage/blob/main/pkg/idtools/idtools_supported.go
+//
+// Copyright (c) Contributors to the Apptainer project, established as
+//   Apptainer a Series of LF Projects LLC.
+// Copyright (c) 2019-2025, Sylabs Inc. All rights reserved.
+// This software is licensed under a 3-clause BSD license. Please consult the
+// LICENSE.md file distributed with the sources of this project regarding your
+// rights to use or distribute this software.
+
+package fakeroot
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+	"unsafe"
+
+	"github.com/sylabs/singularity/v4/internal/pkg/util/user"
+)
+
+/*
+#cgo LDFLAGS: -l subid
+
+#include <shadow/subid.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+struct subid_range singularity_get_range(struct subid_range *ranges, int i)
+{
+	return ranges[i];
+}
+
+#if !defined(SUBID_ABI_MAJOR) || (SUBID_ABI_MAJOR < 4)
+# define subid_get_uid_ranges get_subuid_ranges
+# define subid_get_gid_ranges get_subgid_ranges
+#endif
+*/
+import "C"
+
+func readSubid(user *user.User, isUser bool) ([]*Entry, error) {
+	ret := make([]*Entry, 0)
+	uidstr := fmt.Sprintf("%d", user.UID)
+
+	if user.Name == "ALL" {
+		return nil, errors.New("username ALL not supported")
+	}
+
+	cUsername := C.CString(user.Name)
+	defer C.free(unsafe.Pointer(cUsername))
+
+	cuidstr := C.CString(uidstr)
+	defer C.free(unsafe.Pointer(cuidstr))
+
+	var nRanges C.int
+	var cRanges *C.struct_subid_range
+	if isUser {
+		nRanges = C.subid_get_uid_ranges(cUsername, &cRanges)
+		if nRanges <= 0 {
+			nRanges = C.subid_get_uid_ranges(cuidstr, &cRanges)
+		}
+	} else {
+		nRanges = C.subid_get_gid_ranges(cUsername, &cRanges)
+		if nRanges <= 0 {
+			nRanges = C.subid_get_gid_ranges(cuidstr, &cRanges)
+		}
+	}
+	if nRanges < 0 {
+		return nil, errors.New("cannot read subids")
+	}
+	defer C.free(unsafe.Pointer(cRanges))
+
+	for i := 0; i < int(nRanges); i++ {
+		r := C.singularity_get_range(cRanges, C.int(i))
+		line := fmt.Sprintf("%d:%d:%d", user.UID, r.start, r.count)
+		ret = append(
+			ret,
+			&Entry{
+				UID:      user.UID,
+				Start:    uint32(r.start),
+				Count:    uint32(r.count),
+				disabled: false,
+				line:     line,
+			})
+	}
+	return ret, nil
+}
+
+func readSubuid(user *user.User) ([]*Entry, error) {
+	return readSubid(user, true)
+}
+
+func readSubgid(user *user.User) ([]*Entry, error) {
+	return readSubid(user, false)
+}
+
+func (c *Config) getMappingEntries(user *user.User) ([]*Entry, error) {
+	entries := make([]*Entry, 0)
+	for _, entry := range c.entries {
+		if entry.UID == user.UID {
+			entries = append(entries, entry)
+		}
+	}
+
+	var subidEntries []*Entry
+	var err error
+	if strings.Contains(c.file.Name(), "gid") {
+		subidEntries, err = readSubgid(user)
+	} else {
+		subidEntries, err = readSubuid(user)
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	return append(entries, subidEntries...), nil
+}

internal/pkg/fakeroot/idtools_unsupported.go

@@ -0,0 +1,26 @@
+//go:build !linux || !libsubid || !cgo
+// +build !linux !libsubid !cgo
+
+// Copyright (c) Contributors to the Apptainer project, established as
+//   Apptainer a Series of LF Projects LLC.
+// Copyright (c) 2019-2025, Sylabs Inc. All rights reserved.
+// This software is licensed under a 3-clause BSD license. Please consult the
+// LICENSE.md file distributed with the sources of this project regarding your
+// rights to use or distribute this software.
+
+package fakeroot
+
+import (
+	"github.com/sylabs/singularity/v4/internal/pkg/util/user"
+)
+
+func (c *Config) getMappingEntries(user *user.User) ([]*Entry, error) {
+	entries := make([]*Entry, 0)
+	for _, entry := range c.entries {
+		if entry.UID == user.UID {
+			entries = append(entries, entry)
+		}
+	}
+
+	return entries, nil
+}

mconfig

@@ -1,5 +1,5 @@
 #!/bin/sh -
-# Copyright (c) 2019-2024, Sylabs Inc. All rights reserved.
+# Copyright (c) 2019-2025, Sylabs Inc. All rights reserved.
 # Copyright (c) 2015-2018, Yannick Cote <[email protected]>. All rights reserved.
 # Copyright (c) Contributors to the Apptainer project, established as
 #   Apptainer a Series of LF Projects LLC.
@@ -62,6 +62,7 @@ with_conmon=1
 with_squashfuse=1
 with_suid=1
 with_seccomp_check=1
+with_libsubid=1
 
 builddir=
 prefix=
@@ -117,6 +118,7 @@ usage_args () {
 	echo
 	echo "  Singularity options:"
 	echo "     --without-suid    do not install SUID binary (linux only)"
+  echo "     --without-libsubid do not compile libsubid support even if available (linux only)"
 	echo "     --without-network do not compile/install network plugins (linux only)"
 	echo "     --without-seccomp do not compile/install seccomp support (linux only)"
   echo
@@ -376,6 +378,8 @@ while [ $# -ne 0 ]; do
    verbose=1; shift;;
   --without-suid)
    with_suid=0; shift;;
+  --without-libsubid)
+   with_libsubid=0; shift;;
   --without-network)
    with_network=0; shift;;
   --without-seccomp)
@@ -783,6 +787,11 @@ if [ "$appsec" = "1" ]; then
 	cat $makeit_fragsdir/go_appsec_opts.mk >> $makeit_makefile
 fi
 
+if [ "$libsubid" = "1" ]; then
+	drawline $makeit_fragsdir/go_libsubid_opts.mk
+	cat $makeit_fragsdir/go_libsubid_opts.mk >> $makeit_makefile
+fi
+
 if [ "$build_runtime" = "1" ]; then
 	drawline $makeit_fragsdir/go_runtime_opts.mk
 	cat $makeit_fragsdir/go_runtime_opts.mk >> $makeit_makefile

mlocal/checks/project-post.chk

@@ -518,3 +518,40 @@ config_add_def UNSQUASHFS_PATH \"${unsquashfs_path}\"
 echo
 
 config_add_footer
+
+########################
+# libsubid
+########################
+if [ "$with_libsubid" = "1" ];then
+    printf " checking: libsubid support... "
+    testprog=$makeit_testprogdir/test_libsubid
+    cat > ${testprog}.c << "EOF"
+    #include <shadow/subid.h>
+    #include <stdio.h>
+    #include <stdlib.h>
+
+    const char *Prog = "test";
+    FILE *shadow_logfd = NULL;
+
+    int main() {
+        struct subid_range *ranges = NULL;
+    #if SUBID_ABI_MAJOR >= 4
+        subid_get_uid_ranges("root", &ranges);
+    #else
+        get_subuid_ranges("root", &ranges);
+    #endif
+        free(ranges);
+        return 0;
+    }
+EOF
+    if ! $tgtcc -x c -o $testprog ${testprog}.c -l subid >/dev/null 2>&1; then
+        echo "no"
+    else
+        if ! $testprog; then
+            echo "no"
+        else
+            echo "yes"
+            libsubid=1
+        fi
+    fi
+fi

mlocal/frags/go_libsubid_opts.mk

@@ -0,0 +1,2 @@
+GO_TAGS += libsubid
+GO_TAGS_SUID += libsubid