seccomp: remove dependency on pkg/parsers/kernel

This removes the dependency on the `pkg/parsers/kernel` package, because secomp
only needs to consider Linux (and no parsing is needed for Windows or Darwin kernel
versions).

This patch implements the minimum requirements for this implementation:

- only `kernel` and `major` versions are considered
- `minor` version, `flavor`, and `-rcXX` suffixes are ignored

So, for example:

- `3.4.54.longterm-1` => `kernel: 3`, `major: 4`
- `3.8.0-19-generic` => `kernel: 3`, `major: 8`
- `3.10.0-862.2.3.el7.x86_64` => `kernel: 3`, `major: 10`

Some systems also omit the `minor` and/or have odd-formatted versions. In context
of generating seccomp profiles, both versions below are considered equal;

- `3.12.25-gentoo` => `kernel: 3`, `major: 12`
- `3.12-1-amd64` => `kernel: 3`, `major: 12`

Note that `-rcX` suffixes are also not considered, and thus (e.g.) kernel `5.9-rc1`,
`5.9-rc6` and `5.9` are all considered equal.

The motivation for ignoring "minor" versions and "flavors" is that;

- The upstream kernel only does "kernel.major" releases
- While release-candidates exists for kernel (e.g. 5.9-rc5), we don't expect users
  to write profiles that target a specific release-candidate, and therefore consider
  (e.g.) kernel `5.9-rc1`, `5.9-rc6` and `5.9` to be equal.
- Generally, a seccomp-profile should either be portable, or written for a specific
  infrastructure (in which case the writer of the profile would know if the kernel-flavors
  used does/does not support certain things.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

4 files changed, 200 insertions, 20 deletions

diff --git a/profiles/seccomp/kernel_linux.go b/profiles/seccomp/kernel_linux.go
new file mode 100644
index 0000000000..c2ca03506c
--- /dev/null
+++ b/profiles/seccomp/kernel_linux.go
@@ -0,0 +1,69 @@
+package seccomp
+
+import (
+	"bytes"
+	"fmt"
+	"sync"
+
+	"golang.org/x/sys/unix"
+)
+
+// kernelVersion holds information about the kernel.
+type kernelVersion struct {
+	kernel uint // Version of the kernel (i.e., the "4" in "4.1.2-generic")
+	major  uint // Major revision of the kernel (i.e., the "1" in "4.1.2-generic")
+}
+
+var (
+	currentKernelVersion *kernelVersion
+	kernelVersionError   error
+	once                 sync.Once
+)
+
+// getKernelVersion gets the current kernel version.
+func getKernelVersion() (*kernelVersion, error) {
+	once.Do(func() {
+		var uts unix.Utsname
+		if err := unix.Uname(&uts); err != nil {
+			return
+		}
+		// Remove the \x00 from the release for Atoi to parse correctly
+		currentKernelVersion, kernelVersionError = parseRelease(string(uts.Release[:bytes.IndexByte(uts.Release[:], 0)]))
+	})
+	return currentKernelVersion, kernelVersionError
+}
+
+// parseRelease parses a string and creates a kernelVersion based on it.
+func parseRelease(release string) (*kernelVersion, error) {
+	var version = kernelVersion{}
+
+	// We're only make sure we get the "kernel" and "major revision". Sometimes we have
+	// 3.12.25-gentoo, but sometimes we just have 3.12-1-amd64.
+	_, err := fmt.Sscanf(release, "%d.%d", &version.kernel, &version.major)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse kernel version %q: %w", release, err)
+	}
+	return &version, nil
+}
+
+// kernelGreaterEqualThan checks if the host's kernel version is greater than, or
+// equal to the given kernel version v. Only "kernel version" and "major revision"
+// can be specified (e.g., "3.12") and will be taken into account, which means
+// that 3.12.25-gentoo and 3.12-1-amd64 are considered equal (kernel: 3, major: 12).
+func kernelGreaterEqualThan(v string) (bool, error) {
+	minVersion, err := parseRelease(v)
+	if err != nil {
+		return false, err
+	}
+	kv, err := getKernelVersion()
+	if err != nil {
+		return false, err
+	}
+	if kv.kernel > minVersion.kernel {
+		return true, nil
+	}
+	if kv.kernel == minVersion.kernel && kv.major >= minVersion.major {
+		return true, nil
+	}
+	return false, nil
+}
diff --git a/profiles/seccomp/kernel_linux_test.go b/profiles/seccomp/kernel_linux_test.go
new file mode 100644
index 0000000000..60fb55c416
--- /dev/null
+++ b/profiles/seccomp/kernel_linux_test.go
@@ -0,0 +1,121 @@
+package seccomp
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestGetKernelVersion(t *testing.T) {
+	version, err := getKernelVersion()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if version == nil {
+		t.Fatal("version is nil")
+	}
+	if version.kernel == 0 {
+		t.Fatal("no kernel version")
+	}
+}
+
+// TestParseRelease tests the ParseRelease() function
+func TestParseRelease(t *testing.T) {
+	tests := []struct {
+		in          string
+		out         kernelVersion
+		expectedErr error
+	}{
+		{in: "3.8", out: kernelVersion{kernel: 3, major: 8}},
+		{in: "3.8.0", out: kernelVersion{kernel: 3, major: 8}},
+		{in: "3.8.0-19-generic", out: kernelVersion{kernel: 3, major: 8}},
+		{in: "3.4.54.longterm-1", out: kernelVersion{kernel: 3, major: 4}},
+		{in: "3.10.0-862.2.3.el7.x86_64", out: kernelVersion{kernel: 3, major: 10}},
+		{in: "3.12.8tag", out: kernelVersion{kernel: 3, major: 12}},
+		{in: "3.12-1-amd64", out: kernelVersion{kernel: 3, major: 12}},
+		{in: "3.12foobar", out: kernelVersion{kernel: 3, major: 12}},
+		{in: "99.999.999-19-generic", out: kernelVersion{kernel: 99, major: 999}},
+		{in: "3", expectedErr: fmt.Errorf(`failed to parse kernel version "3": unexpected EOF`)},
+		{in: "3.", expectedErr: fmt.Errorf(`failed to parse kernel version "3.": EOF`)},
+		{in: "3a", expectedErr: fmt.Errorf(`failed to parse kernel version "3a": input does not match format`)},
+		{in: "3.a", expectedErr: fmt.Errorf(`failed to parse kernel version "3.a": expected integer`)},
+		{in: "a", expectedErr: fmt.Errorf(`failed to parse kernel version "a": expected integer`)},
+		{in: "a.a", expectedErr: fmt.Errorf(`failed to parse kernel version "a.a": expected integer`)},
+		{in: "a.a.a-a", expectedErr: fmt.Errorf(`failed to parse kernel version "a.a.a-a": expected integer`)},
+		{in: "-3", expectedErr: fmt.Errorf(`failed to parse kernel version "-3": expected integer`)},
+		{in: "-3.", expectedErr: fmt.Errorf(`failed to parse kernel version "-3.": expected integer`)},
+		{in: "-3.8", expectedErr: fmt.Errorf(`failed to parse kernel version "-3.8": expected integer`)},
+		{in: "-3.-8", expectedErr: fmt.Errorf(`failed to parse kernel version "-3.-8": expected integer`)},
+		{in: "3.-8", expectedErr: fmt.Errorf(`failed to parse kernel version "3.-8": expected integer`)},
+	}
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.in, func(t *testing.T) {
+			version, err := parseRelease(tc.in)
+			if tc.expectedErr != nil {
+				if err == nil {
+					t.Fatal("expected an error")
+				}
+				if err.Error() != tc.expectedErr.Error() {
+					t.Fatalf("expected: %s, got: %s", tc.expectedErr, err)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal("unexpected error:", err)
+			}
+			if version == nil {
+				t.Fatal("version is nil")
+			}
+			if version.kernel != tc.out.kernel || version.major != tc.out.major {
+				t.Fatalf("expected: %d.%d, got: %d.%d", tc.out.kernel, tc.out.major, version.kernel, version.major)
+			}
+		})
+	}
+}
+
+func TestKernelGreaterEqualThan(t *testing.T) {
+	// Get the current kernel version, so that we can make test relative to that
+	v, err := getKernelVersion()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tests := []struct {
+		doc      string
+		in       string
+		expected bool
+	}{
+		{
+			doc:      "same version",
+			in:       fmt.Sprintf("%d.%d", v.kernel, v.major),
+			expected: true,
+		},
+		{
+			doc:      "kernel minus one",
+			in:       fmt.Sprintf("%d.%d", v.kernel-1, v.major),
+			expected: true,
+		},
+		{
+			doc:      "kernel plus one",
+			in:       fmt.Sprintf("%d.%d", v.kernel+1, v.major),
+			expected: false,
+		},
+		{
+			doc:      "major plus one",
+			in:       fmt.Sprintf("%d.%d", v.kernel, v.major+1),
+			expected: false,
+		},
+	}
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.doc+": "+tc.in, func(t *testing.T) {
+			ok, err := kernelGreaterEqualThan(tc.in)
+			if err != nil {
+				t.Fatal("unexpected error:", err)
+			}
+			if ok != tc.expected {
+				t.Fatalf("expected: %v, got: %v", tc.expected, ok)
+			}
+		})
+	}
+}
diff --git a/profiles/seccomp/seccomp.go b/profiles/seccomp/seccomp.go
index 441c37f648..a7a9c5446f 100644
--- a/profiles/seccomp/seccomp.go
+++ b/profiles/seccomp/seccomp.go
@@ -21,9 +21,16 @@ type Architecture struct {
 
 // Filter is used to conditionally apply Seccomp rules
 type Filter struct {
-	Caps      []string `json:"caps,omitempty"`
-	Arches    []string `json:"arches,omitempty"`
-	MinKernel string   `json:"minKernel,omitempty"`
+	Caps   []string `json:"caps,omitempty"`
+	Arches []string `json:"arches,omitempty"`
+
+	// MinKernel describes the minimum kernel version the rule must be applied
+	// on, in the format "<kernel version>.<major revision>" (e.g. "3.12").
+	//
+	// When matching the kernel version of the host, minor revisions, and distro-
+	// specific suffixes are ignored, which means that "3.12.25-gentoo", "3.12-1-amd64",
+	// "3.12", and "3.12-rc5" are considered equal (kernel 3, major revision 12).
+	MinKernel string `json:"minKernel,omitempty"`
 }
 
 // Syscall is used to match a group of syscalls in Seccomp
diff --git a/profiles/seccomp/seccomp_linux.go b/profiles/seccomp/seccomp_linux.go
index c2221115d1..cddf9c4214 100644
--- a/profiles/seccomp/seccomp_linux.go
+++ b/profiles/seccomp/seccomp_linux.go
@@ -8,7 +8,6 @@ import (
 	"fmt"
 	"runtime"
 
-	"github.com/docker/docker/pkg/parsers/kernel"
 	specs "github.com/opencontainers/runtime-spec/specs-go"
 )
 
@@ -177,19 +176,3 @@ func createSpecsSyscall(names []string, action specs.LinuxSeccompAction, args []
 	}
 	return newCall
 }
-
-var currentKernelVersion *kernel.VersionInfo
-
-func kernelGreaterEqualThan(v string) (bool, error) {
-	version, err := kernel.ParseRelease(v)
-	if err != nil {
-		return false, err
-	}
-	if currentKernelVersion == nil {
-		currentKernelVersion, err = kernel.GetKernelVersion()
-		if err != nil {
-			return false, err
-		}
-	}
-	return kernel.CompareKernelVersion(*version, *currentKernelVersion) <= 0, nil
-}