ptp: vmclock: prevent read-only mappings from becoming writable

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "drivers/ptp/ptp_vmclock.c"
                    ],
                    "versions": [
                        {
                            "version": "20503272422693d793b84f88bf23fe4e955d3a33",
                            "lessThan": "5b4f2bec7bea6c04084d720d731bedee7caf878d",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "20503272422693d793b84f88bf23fe4e955d3a33",
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                        {
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                        },
                        {
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                        {
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                            "status": "affected",
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                        {
                            "version": "20503272422693d793b84f88bf23fe4e955d3a33",
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                            "status": "affected",
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                        }
                    ]
                }

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "affected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "drivers/ptp/ptp_vmclock.c"
                    ],
                    "versions": [
                        {
                            "version": "6.13",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "6.13",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.18.47",
                            "lessThanOrEqual": "6.18.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.18.50",
                            "lessThanOrEqual": "6.18.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.1.11",
                            "lessThanOrEqual": "7.1.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.2.1",
                            "lessThanOrEqual": "7.2.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.2.4",
                            "lessThanOrEqual": "7.2.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.3",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
                        }
                    ]
                }