{"id":"CVE-2026-98975","state":"PUBLISHED","title":"xfs: stop exchanging reflink flags when exchanging mappings","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nxfs: stop exchanging reflink flags when exchanging mappings\n\nWhen an exchange covers both files from offset 0 to i_disk_size,\nxmi_can_exchange_reflink_flags() assumes every mapping moved and hands\nthe reflink flag over to the other file.\n\nThat assumption is wrong.  A file can still own shared blocks past\ni_disk_size, e.g. after EXCHANGE_RANGE_TO_EOF sets a smaller size\nwithout unmapping anything.  The flag is cleared anyway, and the next\nwrite to such a block happens in place instead of CoW, corrupting the\nother file that shares it.\n\nCommit a23eca88448e (\"xfs: fix exchange-range reflink flag clearing\nissue with INO1_WRITTEN\") fixed one instance of this.  Rather than add\nanother special case, stop moving the flags.\nxfs_exchmaps_ensure_reflink() already sets the flag on both inodes\nbefore the exchange, so both just keep it.\n\nNothing sets CLEAR_INO{1,2}_REFLINK anymore.  Intents logged by older\nkernels may still carry them; recovery already masks them off, so they\nstay in the log format mask and are ignored.\n\nXFS_IOC_SWAPEXT has the same problem: it moves the reflink flag from\none inode to the other along with the extents.  Just removing that is\nnot enough here: the exchange path flags both inodes up front in\nxfs_exchmaps_ensure_reflink(), but swapext has no such step, so the\ninode receiving the shared extents would be left without the flag.\nSet it on both inodes instead, and make sure both have a CoW fork,\nsince an inode with the reflink flag is expected to have one.\n\nThe flag now stays until FALLOC_FL_UNSHARE_RANGE, xfs_scrub, or a\ntruncate to zero removes it.","publishedAt":"2026-10-23T12:19:48.379Z","updatedAt":"2026-10-24T14:09:45.210Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"f0bc4d134b46607967bda1205ce3226a1bd95f42","status":"affected","lessThan":"1fa2f3a7ef7ee0f2503a4b0afe24bc8c9d0820be","versionType":"git"},{"version":"f0bc4d134b46607967bda1205ce3226a1bd95f42","status":"affected","lessThan":"7d3b9b2c9dc57f93f36c716ab752548cb4db9900","versionType":"git"},{"version":"f0bc4d134b46607967bda1205ce3226a1bd95f42","status":"affected","lessThan":"4756c94260e69ce42612b8220c3614f02f7a11d5","versionType":"git"},{"version":"f0bc4d134b46607967bda1205ce3226a1bd95f42","status":"affected","lessThan":"d84d6c1a7f1e2de9e601703a326a4c1b7b421943","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/xfs/libxfs/xfs_exchmaps.c","fs/xfs/libxfs/xfs_log_format.h","fs/xfs/xfs_bmap_util.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.9","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.9","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.11","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/xfs/libxfs/xfs_exchmaps.c","fs/xfs/libxfs/xfs_log_format.h","fs/xfs/xfs_bmap_util.c"]}],"references":["https://git.kernel.org/stable/c/1fa2f3a7ef7ee0f2503a4b0afe24bc8c9d0820be","https://git.kernel.org/stable/c/7d3b9b2c9dc57f93f36c716ab752548cb4db9900","https://git.kernel.org/stable/c/4756c94260e69ce42612b8220c3614f02f7a11d5","https://git.kernel.org/stable/c/d84d6c1a7f1e2de9e601703a326a4c1b7b421943"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98975.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98975","state":"PUBLISHED","datePublished":"2026-10-23T12:19:48.379Z","dateUpdated":"2026-10-24T14:09:45.210Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.383Z"},"containers":{"cna":{"title":"xfs: stop exchanging reflink flags when exchanging mappings","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nxfs: stop exchanging reflink flags when exchanging mappings\n\nWhen an exchange covers both files from offset 0 to i_disk_size,\nxmi_can_exchange_reflink_flags() assumes every mapping moved and hands\nthe reflink flag over to the other file.\n\nThat assumption is wrong.  A file can still own shared blocks past\ni_disk_size, e.g. after EXCHANGE_RANGE_TO_EOF sets a smaller size\nwithout unmapping anything.  The flag is cleared anyway, and the next\nwrite to such a block happens in place instead of CoW, corrupting the\nother file that shares it.\n\nCommit a23eca88448e (\"xfs: fix exchange-range reflink flag clearing\nissue with INO1_WRITTEN\") fixed one instance of this.  Rather than add\nanother special case, stop moving the flags.\nxfs_exchmaps_ensure_reflink() already sets the flag on both inodes\nbefore the exchange, so both just keep it.\n\nNothing sets CLEAR_INO{1,2}_REFLINK anymore.  Intents logged by older\nkernels may still carry them; recovery already masks them off, so they\nstay in the log format mask and are ignored.\n\nXFS_IOC_SWAPEXT has the same problem: it moves the reflink flag from\none inode to the other along with the extents.  Just removing that is\nnot enough here: the exchange path flags both inodes up front in\nxfs_exchmaps_ensure_reflink(), but swapext has no such step, so the\ninode receiving the shared extents would be left without the flag.\nSet it on both inodes instead, and make sure both have a CoW fork,\nsince an inode with the reflink flag is expected to have one.\n\nThe flag now stays until FALLOC_FL_UNSHARE_RANGE, xfs_scrub, or a\ntruncate to zero removes it."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"f0bc4d134b46607967bda1205ce3226a1bd95f42","status":"affected","lessThan":"1fa2f3a7ef7ee0f2503a4b0afe24bc8c9d0820be","versionType":"git"},{"version":"f0bc4d134b46607967bda1205ce3226a1bd95f42","status":"affected","lessThan":"7d3b9b2c9dc57f93f36c716ab752548cb4db9900","versionType":"git"},{"version":"f0bc4d134b46607967bda1205ce3226a1bd95f42","status":"affected","lessThan":"4756c94260e69ce42612b8220c3614f02f7a11d5","versionType":"git"},{"version":"f0bc4d134b46607967bda1205ce3226a1bd95f42","status":"affected","lessThan":"d84d6c1a7f1e2de9e601703a326a4c1b7b421943","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/xfs/libxfs/xfs_exchmaps.c","fs/xfs/libxfs/xfs_log_format.h","fs/xfs/xfs_bmap_util.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.9","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.9","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.11","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/xfs/libxfs/xfs_exchmaps.c","fs/xfs/libxfs/xfs_log_format.h","fs/xfs/xfs_bmap_util.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/1fa2f3a7ef7ee0f2503a4b0afe24bc8c9d0820be"},{"url":"https://git.kernel.org/stable/c/7d3b9b2c9dc57f93f36c716ab752548cb4db9900"},{"url":"https://git.kernel.org/stable/c/4756c94260e69ce42612b8220c3614f02f7a11d5"},{"url":"https://git.kernel.org/stable/c/d84d6c1a7f1e2de9e601703a326a4c1b7b421943"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - `ioctl(2)` runs `do_vfs_ioctl()`/`vfs_ioctl()` → `xfs_file_ioctl()` → `xfs_ioc_exchange_range()` → `xfs_exchange_mappings()` → patched `xfs_exchmaps_init_intent()`; all causal file descriptors, offsets, and flags are supplied locally.\nAC:L - On a reflink/exchange-range XFS, the attacker can clone a target block, use chosen `TO_EOF` offsets to strand it past `i_disk_size`, perform a full-range exchange so `xmi_can_exchange_reflink_flags()` clears the flag, and `pwrite` the shared block; no race or external event is required.\nPR:L - `xfs_exchange_range()` requires only read-write scratch-file descriptors and `remap_verify_area(..., true)`, with no `capable()` check; FICLONE requires only read access to the protected source and write access to an attacker-owned destination.\nUI:N - The attacker personally performs FICLONERANGE, the crafted `XFS_IOC_EXCHANGE_RANGE` operations, and the final `pwrite`; no victim must mount media, open a file, or take another action.\nS:U - `xfs_exchmaps_clear_reflink()` breaks CoW isolation between inodes on the same XFS host; using the resulting protected-file overwrite for root access is a standard local privilege escalation, not a VM, IOMMU, or other security-authority escape.\nC:H - The attacker can clone a readable SUID-root binary, then make the faulty non-CoW write alter its physical block without modifying its inode or clearing SUID metadata; executing the corrupted binary can yield root and unrestricted access to host-confidential data.\nI:H - After `xfs_exchmaps_clear_reflink()` removes the flag, `xfs_is_cow_inode()` is false and the iomap write path updates the still-shared block in place, permitting persistent attacker-controlled modification of readable protected files without write permission.\nA:H - The same in-place primitive can corrupt readable boot-critical executables, and overwriting a SUID-root binary can provide root control capable of stopping the host, supporting complete availability loss."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-24T14:09:45.210Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.9","versionEndExcluding":"6.12.114"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.9","versionEndExcluding":"6.18.57"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.9","versionEndExcluding":"7.2.11"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.9","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}