Reject duplicate rlimit types in process spec

CHANGELOG.md

@@ -31,6 +31,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   fixed. (#5403, #5487)
 
 ### Changed ###
+- runc now rejects a new container, or a process passed to
+  `runc exec --process`, with duplicate `rlimits` entries of the same type,
+  as required by the runtime-spec. Previously, the last such entry silently
+  took effect. `runc exec` into an existing container is not affected.
+  (#5493, #5494)
 - runc now requires Go 1.26+ to build. (#5413)
 - Updated builds to libseccomp v2.6.1. (#5376)
 - Switched to opencontainers/cgroups v0.1.0, which no longer uses the

exec.go

@@ -217,7 +217,15 @@ func getProcess(cmd *cli.Command, c *libcontainer.Container) (*specs.Process, er
 		if err := json.NewDecoder(f).Decode(&p); err != nil {
 			return nil, err
 		}
-		return &p, validateProcessSpec(&p)
+		if err := validateProcessSpec(&p); err != nil {
+			return nil, err
+		}
+		// The process is new input (not from an existing container's
+		// config.json), so reject duplicate rlimit types here.
+		if err := checkProcessRlimits(&p); err != nil {
+			return nil, err
+		}
+		return &p, nil
 	}
 	// Process from config.json and CLI flags.
 	bundle, ok := utils.SearchLabels(c.Config().Labels, "bundle")

libcontainer/configs/config.go

@@ -8,6 +8,7 @@ import (
 	"errors"
 	"fmt"
 	"os/exec"
+	"slices"
 	"strconv"
 	"strings"
 	"time"
@@ -633,3 +634,16 @@ func (c *Command) Run(s *specs.State) error {
 		return fmt.Errorf("hook ran past specified timeout of %.1fs", c.Timeout.Seconds())
 	}
 }
+
+// CheckRlimits returns an error if limits contain more than one entry
+// of the same type.
+func CheckRlimits(limits []Rlimit) error {
+	// There are only a few rlimit types, so a linear search is cheaper
+	// than building a map.
+	for i, l := range limits {
+		if slices.ContainsFunc(limits[:i], func(r Rlimit) bool { return r.Type == l.Type }) {
+			return fmt.Errorf("duplicate rlimit type: %d", l.Type)
+		}
+	}
+	return nil
+}

libcontainer/configs/validate/validator.go

@@ -34,6 +34,7 @@ func Validate(config *configs.Config) error {
 		scheduler,
 		ioPriority,
 		memoryPolicy,
+		rlimits,
 	}
 	for _, c := range checks {
 		if err := c(config); err != nil {
@@ -506,3 +507,9 @@ func memoryPolicy(config *configs.Config) error {
 	}
 	return nil
 }
+
+// rlimits checks that there is no more than one entry per rlimit type,
+// as required by the runtime-spec.
+func rlimits(config *configs.Config) error {
+	return configs.CheckRlimits(config.Rlimits)
+}

libcontainer/configs/validate/validator_test.go

@@ -1077,3 +1077,39 @@ func TestDevValidName(t *testing.T) {
 		})
 	}
 }
+
+func TestValidateRlimits(t *testing.T) {
+	for _, tc := range []struct {
+		name    string
+		rlimits []configs.Rlimit
+		isErr   bool
+	}{
+		{name: "none"},
+		{
+			name: "distinct",
+			rlimits: []configs.Rlimit{
+				{Type: unix.RLIMIT_NOFILE, Soft: 32, Hard: 64},
+				{Type: unix.RLIMIT_CORE},
+			},
+		},
+		{
+			name: "duplicate",
+			rlimits: []configs.Rlimit{
+				{Type: unix.RLIMIT_NOFILE, Soft: 32, Hard: 64},
+				{Type: unix.RLIMIT_NOFILE, Soft: 48, Hard: 64},
+			},
+			isErr: true,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			config := &configs.Config{Rootfs: "/var", Rlimits: tc.rlimits}
+			err := Validate(config)
+			if tc.isErr && err == nil {
+				t.Fatal("expected error, got nil")
+			}
+			if !tc.isErr && err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+		})
+	}
+}

libcontainer/container_linux.go

@@ -376,6 +376,9 @@ func (c *Container) start(process *Process) (retErr error) {
 		if c.initProcessStartTime != 0 {
 			return errors.New("container already has init process")
 		}
+		if err := configs.CheckRlimits(process.Rlimits); err != nil {
+			return err
+		}
 		if err := c.createExecFifo(); err != nil {
 			return err
 		}

tests/integration/exec.bats

@@ -424,3 +424,40 @@ EOF
 	[ "$status" -eq 0 ]
 	[ "${lines[0]}" = "/home/tempuser" ]
 }
+
+# Duplicate rlimit types are rejected for new containers and for
+# "runc exec --process", but not for an existing container whose
+# config.json (created by an older runc) has them.
+@test "runc exec [duplicate rlimits in existing container config]" {
+	runc run -d --console-socket "$CONSOLE_SOCKET" test_busybox
+	[ "$status" -eq 0 ]
+
+	# Simulate a config.json from an older runc.
+	update_config '.process.rlimits = [
+		{"type": "RLIMIT_NOFILE", "soft": 32, "hard": 64},
+		{"type": "RLIMIT_NOFILE", "soft": 48, "hard": 64}
+	]'
+
+	runc exec test_busybox true
+	[ "$status" -eq 0 ]
+
+	proc='{"terminal": false, "cwd": "/", "args": ["true"],
+		"rlimits": [
+			{"type": "RLIMIT_NOFILE", "soft": 32, "hard": 64},
+			{"type": "RLIMIT_NOFILE", "soft": 48, "hard": 64}
+		]}'
+	runc exec --process <(echo "$proc") test_busybox
+	[ "$status" -ne 0 ]
+	[[ "$output" == *"duplicate rlimit type"* ]]
+}
+
+@test "runc run [duplicate rlimits]" {
+	update_config '.process.rlimits = [
+		{"type": "RLIMIT_NOFILE", "soft": 32, "hard": 64},
+		{"type": "RLIMIT_NOFILE", "soft": 48, "hard": 64}
+	]'
+
+	runc run test_busybox
+	[ "$status" -ne 0 ]
+	[[ "$output" == *"duplicate rlimit type"* ]]
+}

utils_linux.go

@@ -7,6 +7,7 @@ import (
 	"net"
 	"os"
 	"path/filepath"
+	"slices"
 	"strconv"
 
 	"github.com/opencontainers/runtime-spec/specs-go"
@@ -351,6 +352,16 @@ func (r *runner) checkTerminal(config *specs.Process) error {
 	return nil
 }
 
+// checkProcessRlimits returns an error if p has duplicate rlimit types.
+func checkProcessRlimits(p *specs.Process) error {
+	for i, r := range p.Rlimits {
+		if slices.ContainsFunc(p.Rlimits[:i], func(x specs.POSIXRlimit) bool { return x.Type == r.Type }) {
+			return fmt.Errorf("duplicate rlimit type: %s", r.Type)
+		}
+	}
+	return nil
+}
+
 func validateProcessSpec(spec *specs.Process) error {
 	if spec == nil {
 		return errors.New("process property must not be empty")

utils_linux_test.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/opencontainers/runtime-spec/specs-go"
+)
+
+func TestCheckProcessRlimits(t *testing.T) {
+	for _, tc := range []struct {
+		name    string
+		rlimits []specs.POSIXRlimit
+		isErr   bool
+	}{
+		{name: "none"},
+		{
+			name: "distinct",
+			rlimits: []specs.POSIXRlimit{
+				{Type: "RLIMIT_NOFILE", Soft: 32, Hard: 64},
+				{Type: "RLIMIT_CORE"},
+			},
+		},
+		{
+			name: "duplicate",
+			rlimits: []specs.POSIXRlimit{
+				{Type: "RLIMIT_NOFILE", Soft: 32, Hard: 64},
+				{Type: "RLIMIT_NOFILE", Soft: 48, Hard: 64},
+			},
+			isErr: true,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			err := checkProcessRlimits(&specs.Process{Rlimits: tc.rlimits})
+			if tc.isErr && err == nil {
+				t.Fatal("expected error, got nil")
+			}
+			if !tc.isErr && err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+		})
+	}
+}