{"id":"CVE-2026-90260","state":"PUBLISHED","title":"btrfs: zoned: don't clobber the extent buffer when zeroing it out","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: zoned: don't clobber the extent buffer when zeroing it out\n\nOn a zoned filesystem a freed-but-still-dirty tree block is written out\nas zeros (EXTENT_BUFFER_ZONED_ZEROOUT) only to keep the zone write\npointer advancing. btree_csum_one_bio() implemented this by memzeroing\nthe extent buffer's own folios before submission.\n\nThat destroys the in-memory buffer while it may still be referenced. In\nparticular btrfs_free_tree_block() can run on it afterwards and reads\nthe header to add a delayed reference; once the header has been zeroed\nit frees bytenr 0 and corrupts the extent tree (the\nbtrfs_header_bytenr(buf) != 0 ASSERT in btrfs_free_tree_block(), or an\n\"unable to find ref\" abort). It is flaky and reproduces under fsstress,\ne.g. generic/461 and generic/013.\n\nWrite the zeros to disk from the shared zero page instead and leave the\nextent buffer content untouched, so any later reference - including the\ndelayed reference from btrfs_free_tree_block() - still sees a valid\nheader. end_bbio_meta_write() now clears writeback on the buffer's own\nfolios, as the bio no longer carries them.","publishedAt":"2026-09-17T16:07:58.102Z","updatedAt":"2026-10-21T12:50:42.251Z","severity":{"score":7.1,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"aa6313e6ff2bfbf736a2739047bba355d8241584","status":"affected","lessThan":"efa5084d08030aa557fdefa3e4a73b2501b7d207","versionType":"git"},{"version":"aa6313e6ff2bfbf736a2739047bba355d8241584","status":"affected","lessThan":"92484ad014f2e2b0e0e7bbc1610951e978cf557c","versionType":"git"},{"version":"aa6313e6ff2bfbf736a2739047bba355d8241584","status":"affected","lessThan":"98e3747587f9f87f010d8d7e55786216249a94af","versionType":"git"},{"version":"aa6313e6ff2bfbf736a2739047bba355d8241584","status":"affected","lessThan":"db4b9eefc8ee0bcaeee4d5e6a7313905f6a2fe7c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/disk-io.c","fs/btrfs/extent_io.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.8","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.52","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.6","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/btrfs/disk-io.c","fs/btrfs/extent_io.c"]}],"references":["https://git.kernel.org/stable/c/efa5084d08030aa557fdefa3e4a73b2501b7d207","https://git.kernel.org/stable/c/92484ad014f2e2b0e0e7bbc1610951e978cf557c","https://git.kernel.org/stable/c/98e3747587f9f87f010d8d7e55786216249a94af","https://git.kernel.org/stable/c/db4b9eefc8ee0bcaeee4d5e6a7313905f6a2fe7c"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:34.582Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/90xxx/CVE-2026-90260.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-90260","state":"PUBLISHED","datePublished":"2026-09-17T16:07:58.102Z","dateUpdated":"2026-10-21T12:50:42.251Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.796Z"},"containers":{"cna":{"title":"btrfs: zoned: don't clobber the extent buffer when zeroing it out","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: zoned: don't clobber the extent buffer when zeroing it out\n\nOn a zoned filesystem a freed-but-still-dirty tree block is written out\nas zeros (EXTENT_BUFFER_ZONED_ZEROOUT) only to keep the zone write\npointer advancing. btree_csum_one_bio() implemented this by memzeroing\nthe extent buffer's own folios before submission.\n\nThat destroys the in-memory buffer while it may still be referenced. In\nparticular btrfs_free_tree_block() can run on it afterwards and reads\nthe header to add a delayed reference; once the header has been zeroed\nit frees bytenr 0 and corrupts the extent tree (the\nbtrfs_header_bytenr(buf) != 0 ASSERT in btrfs_free_tree_block(), or an\n\"unable to find ref\" abort). It is flaky and reproduces under fsstress,\ne.g. generic/461 and generic/013.\n\nWrite the zeros to disk from the shared zero page instead and leave the\nextent buffer content untouched, so any later reference - including the\ndelayed reference from btrfs_free_tree_block() - still sees a valid\nheader. end_bbio_meta_write() now clears writeback on the buffer's own\nfolios, as the bio no longer carries them."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"aa6313e6ff2bfbf736a2739047bba355d8241584","status":"affected","lessThan":"efa5084d08030aa557fdefa3e4a73b2501b7d207","versionType":"git"},{"version":"aa6313e6ff2bfbf736a2739047bba355d8241584","status":"affected","lessThan":"92484ad014f2e2b0e0e7bbc1610951e978cf557c","versionType":"git"},{"version":"aa6313e6ff2bfbf736a2739047bba355d8241584","status":"affected","lessThan":"98e3747587f9f87f010d8d7e55786216249a94af","versionType":"git"},{"version":"aa6313e6ff2bfbf736a2739047bba355d8241584","status":"affected","lessThan":"db4b9eefc8ee0bcaeee4d5e6a7313905f6a2fe7c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/disk-io.c","fs/btrfs/extent_io.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.8","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.52","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.6","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/btrfs/disk-io.c","fs/btrfs/extent_io.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/efa5084d08030aa557fdefa3e4a73b2501b7d207"},{"url":"https://git.kernel.org/stable/c/92484ad014f2e2b0e0e7bbc1610951e978cf557c"},{"url":"https://git.kernel.org/stable/c/98e3747587f9f87f010d8d7e55786216249a94af"},{"url":"https://git.kernel.org/stable/c/db4b9eefc8ee0bcaeee4d5e6a7313905f6a2fe7c"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H","baseScore":7.1,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The trigger is local VFS syscalls on a mounted zoned btrfs: unlink → btrfs_unlink() → btrfs_del_items() → btrfs_clear_buffer_dirty() sets EXTENT_BUFFER_ZONED_ZEROOUT, then fsync → btrfs_sync_file() → btree_writepages() → write_one_eb() → btree_csum_one_bio(). No network protocol carries the data that causes the clobber.\nAC:L - The attacker drives both sides: unlink/write churn that sets ZONED_ZEROOUT in btrfs_clear_buffer_dirty() while leaving DIRTY set, and fsync or btrfs_btree_balance_dirty() running btree_writepages(). lock_extent_buffer_for_io() drops the tree lock before the memzero, and btrfs_del_leaf() unlocks before btrfs_free_tree_block() reads the header.\nPR:L - btrfs_unlink() and btrfs_sync_file() have no capability check; an unprivileged user with write access on the already-mounted zoned volume can COW-free tree blocks and kick metadata writeback (fsync or the btrfs_btree_balance_dirty() at the end of btrfs_unlink()).\nUI:N - The attacker performs the unlink/write/fsync sequence themselves on files they can write; this is a runtime COW/writeback race on a legitimate zoned btrfs (reproduced by fsstress generic/461 and generic/013), not a crafted image a victim must mount.\nS:U - The clobbered extent-buffer folios and the bad delayed refs stay inside this mount's btrfs metadata in the host kernel; there is no KVM/Xen guest-to-host, IOMMU, or sandbox boundary crossing.\nC:N - btree_csum_one_bio() calls memzero_extent_buffer(eb, 0, eb->len), which memset_extent_buffer() restricts to that buffer's own folios via check_eb_range(); the overwrite is zeros, not an out-of-bounds read or kernel-pointer leak.\nI:H - After the header is zeroed, btrfs_free_tree_block() queues a BTRFS_DROP_DELAYED_REF with owning_root=btrfs_header_owner(buf)==0 and level=btrfs_header_level(buf)==0, so __btrfs_free_extent() applies a mismatched backref to the shared extent tree and corrupts metadata for every file on the volume.\nA:H - The mismatched delayed ref hits abort_and_dump() → btrfs_abort_transaction(-EUCLEAN) → __btrfs_handle_fs_error() → btrfs_set_sb_rdonly(), forcing the whole filesystem read-only; with CONFIG_BTRFS_ASSERT, ASSERT(btrfs_header_bytenr(buf) != 0) in btrfs_free_tree_block() panics."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-21T12:50:42.251Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"6.12.114"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"6.18.52"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"7.2.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}