{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-93798", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-18T17:59:28.789Z", "datePublished": "2026-09-24T16:02:31.291Z", "dateUpdated": "2026-10-03T10:57:32.550Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-03T10:57:32.550Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix reloc root cleanup in merge_reloc_roots()\n\nIf the root we got has zero root refs in its root item, we are resetting\nthe root's ->reloc_root without using barriers like we do everywhere else.\nSashiko complained about this while reviewing another patch, and it's\ncorrect (see the Link tag below).\n\nAlso, we should not clear BTRFS_ROOT_DEAD_RELOC_TREE from the root unless\nthe root points to the reloc root we have.\n\nFix this by using clear_reloc_root(), which issues the memory barrier\nafter setting the root's ->reloc_root to NULL and before clearing the bit\nBTRFS_ROOT_DEAD_RELOC_TREE from the root." } ], "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 - merge_reloc_roots() is reached from local VFS activity: unlink/write call btrfs_update_block_group() which btrfs_mark_bg_to_reclaim(); btrfs_reclaim_bgs_work() then runs btrfs_relocate_chunk()->btrfs_relocate_block_group()->relocate_block_group()->prepare_to_merge()->merge_reloc_roots(). No network protocol supplies the causing state.\nAC:L - When relocate_block_group() fails (the attacker can force ENOSPC via extra allocations), prepare_to_merge() leaves reloc roots at 0 refs and merge_reloc_roots() NULLs root->reloc_root then clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE) without smp_wmb(). Concurrent writes invoke btrfs_init_reloc_root()/have_reloc_root() on that same root, so the attacker drives both sides.\nPR:L - BTRFS_IOC_BALANCE requires capable(CAP_SYS_ADMIN), but btrfs_buffered_write() and unlink used to mark a block group reclaimable have no capability gate. btrfs_fs_type lacks FS_USERNS_MOUNT, so the volume is admin-mounted, yet any unprivileged uid with write permission on that mount can induce reclaim into merge_reloc_roots().\nUI:N - The attacker induces the 0-ref merge_reloc_roots() cleanup with their own writes and deletions on a btrfs they can already write, then races have_reloc_root() with further writes or btrfs_ioctl_snap_create(); no second user needs to mount an image or run balance.\nS:U - The use-after-free is of the struct btrfs_root stored in fs_root->reloc_root inside the same host kernel that mounted the volume; merge_reloc_roots() does not cross a VM, IOMMU, or sandbox authority.\nC:H - Missing smp_wmb() in merge_reloc_roots() lets have_reloc_root() see BTRFS_ROOT_DEAD_RELOC_TREE already clear while still loading the old root->reloc_root pointer; btrfs_should_ignore_reloc_root() then reads reloc_root->commit_root after the matching btrfs_put_root() dropped that reloc root.\nI:H - The same stale reloc_root is written by btrfs_init_reloc_root() via btrfs_set_root_last_trans() and by commit_fs_roots()->btrfs_update_reloc_root() which mutates reloc_root->root_item, giving a write-after-free of struct btrfs_root.\nA:H - Using the dangling reloc_root after merge_reloc_roots()'s btrfs_put_root() oopses; if clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE) becomes visible while the pointer still refers to the 0-ref tree, btrfs_reloc_pre_snapshot() hits BUG_ON(btrfs_root_refs(&root->root_item)==0)." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/btrfs/relocation.c" ], "versions": [ { "version": "1dae7e0e58b484eaa43d530f211098fdeeb0f404", "lessThan": "29531470b1bf1e8bd2df4941fe913106edbca615", "status": "affected", "versionType": "git" }, { "version": "1dae7e0e58b484eaa43d530f211098fdeeb0f404", "lessThan": "415f8665a969d3c906e4fd7c90fcbb4b357886f6", "status": "affected", "versionType": "git" }, { "version": "1dae7e0e58b484eaa43d530f211098fdeeb0f404", "lessThan": "ee695a968aa73b1e67ccbf2133dc0e54381d32b2", "status": "affected", "versionType": "git" }, { "version": "1dae7e0e58b484eaa43d530f211098fdeeb0f404", "lessThan": "0bc25f0a2d1b3e0a691431c4d7aef36afcd527c5", "status": "affected", "versionType": "git" }, { "version": "1dae7e0e58b484eaa43d530f211098fdeeb0f404", "lessThan": "ab48583aa9948205ff9a6470e23dbff74c565e24", "status": "affected", "versionType": "git" }, { "version": "1dae7e0e58b484eaa43d530f211098fdeeb0f404", "lessThan": "63d6b1f04cd91c825329712aa526215ffa5d11ca", "status": "affected", "versionType": "git" }, { "version": "1dae7e0e58b484eaa43d530f211098fdeeb0f404", "lessThan": "b78fe9563e2d5ae47805f1e5dc722c91fd30e1f8", "status": "affected", "versionType": "git" }, { "version": "ee08663380ffd5a45a1c87580fbc305e8413c235", "status": "affected", "versionType": "git" }, { "version": "33823378ff2b510fd7b566f25bb18438aeb9b23b", "status": "affected", "versionType": "git" }, { "version": "5.4.54", "lessThan": "5.5", "status": "affected", "versionType": "semver" }, { "version": "5.7.11", "lessThan": "5.8", "status": "affected", "versionType": "semver" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/btrfs/relocation.c" ], "versions": [ { "version": "5.8", "status": "affected" }, { "version": "0", "lessThan": "5.8", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.271", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.222", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.189", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.158", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.111", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.53", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.8", "versionEndExcluding": "5.10.271" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.8", "versionEndExcluding": "5.15.222" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.8", "versionEndExcluding": "6.1.189" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.8", "versionEndExcluding": "6.6.158" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.8", "versionEndExcluding": "6.12.111" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.8", "versionEndExcluding": "6.18.53" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.8", "versionEndExcluding": "7.2" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.4.54" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.7.11" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/29531470b1bf1e8bd2df4941fe913106edbca615" }, { "url": "https://git.kernel.org/stable/c/415f8665a969d3c906e4fd7c90fcbb4b357886f6" }, { "url": "https://git.kernel.org/stable/c/ee695a968aa73b1e67ccbf2133dc0e54381d32b2" }, { "url": "https://git.kernel.org/stable/c/0bc25f0a2d1b3e0a691431c4d7aef36afcd527c5" }, { "url": "https://git.kernel.org/stable/c/ab48583aa9948205ff9a6470e23dbff74c565e24" }, { "url": "https://git.kernel.org/stable/c/63d6b1f04cd91c825329712aa526215ffa5d11ca" }, { "url": "https://git.kernel.org/stable/c/b78fe9563e2d5ae47805f1e5dc722c91fd30e1f8" } ], "title": "btrfs: fix reloc root cleanup in merge_reloc_roots()", "x_generator": { "engine": "bippy-1.2.0" } } } }