{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2022-49075","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2025-02-26T01:49:39.245Z","datePublished":"2025-02-26T01:54:38.757Z","dateUpdated":"2026-08-05T08:53:44.398Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T08:53:44.398Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix qgroup reserve overflow the qgroup limit\n\nWe use extent_changeset->bytes_changed in qgroup_reserve_data() to record\nhow many bytes we set for EXTENT_QGROUP_RESERVED state. Currently the\nbytes_changed is set as \"unsigned int\", and it will overflow if we try to\nfallocate a range larger than 4GiB. The result is we reserve less bytes\nand eventually break the qgroup limit.\n\nUnlike regular buffered/direct write, which we use one changeset for\neach ordered extent, which can never be larger than 256M.  For\nfallocate, we use one changeset for the whole range, thus it no longer\nrespects the 256M per extent limit, and caused the problem.\n\nThe following example test script reproduces the problem:\n\n  $ cat qgroup-overflow.sh\n  #!/bin/bash\n\n  DEV=/dev/sdj\n  MNT=/mnt/sdj\n\n  mkfs.btrfs -f $DEV\n  mount $DEV $MNT\n\n  # Set qgroup limit to 2GiB.\n  btrfs quota enable $MNT\n  btrfs qgroup limit 2G $MNT\n\n  # Try to fallocate a 3GiB file. This should fail.\n  echo\n  echo \"Try to fallocate a 3GiB file...\"\n  fallocate -l 3G $MNT/3G.file\n\n  # Try to fallocate a 5GiB file.\n  echo\n  echo \"Try to fallocate a 5GiB file...\"\n  fallocate -l 5G $MNT/5G.file\n\n  # See we break the qgroup limit.\n  echo\n  sync\n  btrfs qgroup show -r $MNT\n\n  umount $MNT\n\nWhen running the test:\n\n  $ ./qgroup-overflow.sh\n  (...)\n\n  Try to fallocate a 3GiB file...\n  fallocate: fallocate failed: Disk quota exceeded\n\n  Try to fallocate a 5GiB file...\n\n  qgroupid         rfer         excl     max_rfer\n  --------         ----         ----     --------\n  0/5           5.00GiB      5.00GiB      2.00GiB\n\nSince we have no control of how bytes_changed is used, it's better to\nset it to u64."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H","baseScore":8.1,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - The vulnerable fallocate→btrfs_qgroup_reserve_data path is invoked by in-kernel network servers: nfsd4_allocate (nfsd4_vfs_fallocate) and ksmbd vfs_fallocate on btrfs exports. Worst reasonable deployment is a multi-tenant NAS (e.g. Synology-style btrfs+qgroups over SMB/NFS) where a remote peer triggers the overflow with a >4GiB allocate.\nAC:L - The attacker fully controls the trigger by issuing a single fallocate/ALLOCATE larger than 4GiB on a writable file; unsigned-int wrap of bytes_changed is deterministic, and qgroups are routinely enabled in the multi-tenant/NAS deployments where this limit matters.\nPR:L - Exploitation needs only an authenticated principal with write access (local unprivileged user, or NFS WR_STATE / SMB write after session setup). Enabling quotas requires CAP_SYS_ADMIN, but bypassing an already-enforced qgroup does not.\nUI:N - The attacker drives fallocate/ALLOCATE themselves against a file they can write; no separate victim action or privileged helper is required once the btrfs volume with qgroups is already serving.\nS:U - Impact stays within the host kernel’s filesystem/quota authority for that volume; no VM escape, IOMMU bypass, or cross-sandbox boundary is crossed.\nC:N - The bug is pure qgroup accounting underflow from a 32-bit bytes_changed wrap; it discloses no kernel memory, file contents, or other tenants’ data.\nI:H - The overflow causes qgroup_reserve() to reserve the wrapped (far smaller) amount, completely defeating the qgroup limit so the attacker can allocate and persist arbitrary extents beyond their authorized quota—a complete loss of that isolation protection with attacker-controlled writes.\nA:H - Bypassing qgroup caps lets the attacker consume free space belonging to other tenants on the shared volume until ENOSPC, fully denying write service to co-tenants; free-path WARN_ON desync under panic_on_warn can also take the host down."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/extent_io.h"],"versions":[{"version":"7bc329c1836866ffac8b2613f780a51b3ffe786d","lessThan":"0355387ea5b02d353c9415613fab908fac5c52a6","status":"affected","versionType":"git"},{"version":"7bc329c1836866ffac8b2613f780a51b3ffe786d","lessThan":"f3d97b22a708bf9e3f3ac2ba232bcefd0b0c136b","status":"affected","versionType":"git"},{"version":"7bc329c1836866ffac8b2613f780a51b3ffe786d","lessThan":"44277c50fdba5019ca25bfad1b71e2561b0de11b","status":"affected","versionType":"git"},{"version":"7bc329c1836866ffac8b2613f780a51b3ffe786d","lessThan":"82ae73ac963cee877ce34f7c31b2b456b516e96c","status":"affected","versionType":"git"},{"version":"7bc329c1836866ffac8b2613f780a51b3ffe786d","lessThan":"4b98799e181b4326a613108cf37acc1f55d21b45","status":"affected","versionType":"git"},{"version":"7bc329c1836866ffac8b2613f780a51b3ffe786d","lessThan":"6bfff81286d4491f02dad7814bae5c77c9ad2320","status":"affected","versionType":"git"},{"version":"7bc329c1836866ffac8b2613f780a51b3ffe786d","lessThan":"7941b74ed49b6db25efbef2256ebef843c11a010","status":"affected","versionType":"git"},{"version":"7bc329c1836866ffac8b2613f780a51b3ffe786d","lessThan":"b642b52d0b50f4d398cb4293f64992d0eed2e2ce","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/btrfs/extent_io.h"],"versions":[{"version":"4.13","status":"affected"},{"version":"0","lessThan":"4.13","status":"unaffected","versionType":"semver"},{"version":"4.14.276","lessThanOrEqual":"4.14.*","status":"unaffected","versionType":"semver"},{"version":"4.19.238","lessThanOrEqual":"4.19.*","status":"unaffected","versionType":"semver"},{"version":"5.4.189","lessThanOrEqual":"5.4.*","status":"unaffected","versionType":"semver"},{"version":"5.10.111","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.15.34","lessThanOrEqual":"5.15.*","status":"unaffected","versionType":"semver"},{"version":"5.16.20","lessThanOrEqual":"5.16.*","status":"unaffected","versionType":"semver"},{"version":"5.17.3","lessThanOrEqual":"5.17.*","status":"unaffected","versionType":"semver"},{"version":"5.18","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":"4.13","versionEndExcluding":"4.14.276"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.13","versionEndExcluding":"4.19.238"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.13","versionEndExcluding":"5.4.189"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.13","versionEndExcluding":"5.10.111"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.13","versionEndExcluding":"5.15.34"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.13","versionEndExcluding":"5.16.20"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.13","versionEndExcluding":"5.17.3"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.13","versionEndExcluding":"5.18"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/0355387ea5b02d353c9415613fab908fac5c52a6"},{"url":"https://git.kernel.org/stable/c/f3d97b22a708bf9e3f3ac2ba232bcefd0b0c136b"},{"url":"https://git.kernel.org/stable/c/44277c50fdba5019ca25bfad1b71e2561b0de11b"},{"url":"https://git.kernel.org/stable/c/82ae73ac963cee877ce34f7c31b2b456b516e96c"},{"url":"https://git.kernel.org/stable/c/4b98799e181b4326a613108cf37acc1f55d21b45"},{"url":"https://git.kernel.org/stable/c/6bfff81286d4491f02dad7814bae5c77c9ad2320"},{"url":"https://git.kernel.org/stable/c/7941b74ed49b6db25efbef2256ebef843c11a010"},{"url":"https://git.kernel.org/stable/c/b642b52d0b50f4d398cb4293f64992d0eed2e2ce"}],"title":"btrfs: fix qgroup reserve overflow the qgroup limit","x_generator":{"engine":"bippy-1.2.0"}}}}