bug_fix: updating the parseKernelVersion() function

Previously, Cilium expects the kernel version to always have 3 digits.
However, the kernel is perfectly allowed to have only 2 or even only 1 digit
for the version number.
https://github.com/torvalds/linux/blob/35a4474b5c3dd4315f72bd53e87b97f128d9bb3d/Makefile#L367

This patch makes changes to the following :
- cilium/pkg/version/version_unix.go - updated the parseKernelVersion() to
handle single as well double digit kernel versions along with the standard
kernel versioning.
- cilium/pkg/version/version_unix_test.go - added additional test cases

Fixes: #30630

Signed-off-by: MeherRushi <meherrushi2@gmail.com>

pkg/version/version_unix.go

@@ -18,23 +18,33 @@ import (
 
 func parseKernelVersion(ver string) (semver.Version, error) {
 	verStrs := strings.Split(ver, ".")
-	switch {
-	case len(verStrs) < 2:
+
+	// We are assuming the kernel version will be one of the following:
+	// 4.9.17-040917-generic or 4.9-040917-generic or 4-generic
+	// So as observed, the kernel value is N.N.N-m or N.N-m or N-m
+	// This implies the len(verStrs) should be between 1 and 3
+
+	if len(verStrs) < 1 || len(verStrs) > 3 {
 		return semver.Version{}, fmt.Errorf("unable to get kernel version from %q", ver)
-	case len(verStrs) < 3:
-		verStrs = append(verStrs, "0")
 	}
-	// We are assuming the kernel version will be something as:
-	// 4.9.17-040917-generic
 
-	// If verStrs is []string{ "4", "9", "17-040917-generic" }
-	// then we need to retrieve patch number.
-	patch := regexp.MustCompilePOSIX(`^[0-9]+`).FindString(verStrs[2])
+	// Given the observations, we use regular expression to extract
+	// the patch number from the last element of the verStrs array and
+	// append "0" to the verStrs array in case the until its length is
+	// 3 as in all cases we want to return from this function :
+	// Major.Minor.PatchNumber
+
+	patch := regexp.MustCompilePOSIX(`^[0-9]+`).FindString(verStrs[len(verStrs)-1])
 	if patch == "" {
-		verStrs[2] = "0"
+		verStrs[len(verStrs)-1] = "0"
 	} else {
-		verStrs[2] = patch
+		verStrs[len(verStrs)-1] = patch
 	}
+
+	for len(verStrs) < 3 {
+		verStrs = append(verStrs, "0")
+	}
+
 	return versioncheck.Version(strings.Join(verStrs[:3], "."))
 }
 

pkg/version/version_unix_test.go

@@ -30,6 +30,11 @@ func (vs *VersionSuite) TestParseKernelVersion(c *C) {
 		{"4.14.0-rc7+", mustHaveVersion("4.14.0")},
 		{"4.9.17-040917-generic", mustHaveVersion("4.9.17")},
 		{"4.9.generic", mustHaveVersion("4.9.0")},
+		{"6.5.0-15-generic", mustHaveVersion("6.5.0")},
+		{"6.7-amd64", mustHaveVersion("6.7.0")},
+		{"6.5-15-generic", mustHaveVersion("6.5.0")},
+		{"6.5.2-rc8+", mustHaveVersion("6.5.2")},
+		{"6-generic", mustHaveVersion("6.0.0")},
 	}
 	for _, tt := range flagtests {
 		s, err := parseKernelVersion(tt.in)