exfat: fix valid_size extension over a shared writable mapping

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "fs/exfat/exfat_fs.h",
                        "fs/exfat/file.c",
                        "fs/exfat/iomap.c"
                    ],
                    "versions": [
                        {
                            "version": "82a81a7352bcf5f2756ac33d47ee0582737e9a85",
                            "lessThan": "24f20986b253c3e4eb13ebe3c2007d1d352408a6",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "82a81a7352bcf5f2756ac33d47ee0582737e9a85",
                            "lessThan": "1135704ed22f54873eb0498a232611d9eca30dd4",
                            "status": "affected",
                            "versionType": "git"
                        }
                    ]
                }

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "affected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "fs/exfat/exfat_fs.h",
                        "fs/exfat/file.c",
                        "fs/exfat/iomap.c"
                    ],
                    "versions": [
                        {
                            "version": "7.2",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "7.2",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.2.6",
                            "lessThanOrEqual": "7.2.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.3",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
                        }
                    ]
                }