{"id":"CVE-2021-47189","state":"PUBLISHED","title":"btrfs: fix memory ordering between normal and ordered work functions","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix memory ordering between normal and ordered work functions\n\nOrdered work functions aren't guaranteed to be handled by the same thread\nwhich executed the normal work functions. The only way execution between\nnormal/ordered functions is synchronized is via the WORK_DONE_BIT,\nunfortunately the used bitops don't guarantee any ordering whatsoever.\n\nThis manifested as seemingly inexplicable crashes on ARM64, where\nasync_chunk::inode is seen as non-null in async_cow_submit which causes\nsubmit_compressed_extents to be called and crash occurs because\nasync_chunk::inode suddenly became NULL. The call trace was similar to:\n\n    pc : submit_compressed_extents+0x38/0x3d0\n    lr : async_cow_submit+0x50/0xd0\n    sp : ffff800015d4bc20\n\n    <registers omitted for brevity>\n\n    Call trace:\n     submit_compressed_extents+0x38/0x3d0\n     async_cow_submit+0x50/0xd0\n     run_ordered_work+0xc8/0x280\n     btrfs_work_helper+0x98/0x250\n     process_one_work+0x1f0/0x4ac\n     worker_thread+0x188/0x504\n     kthread+0x110/0x114\n     ret_from_fork+0x10/0x18\n\nFix this by adding respective barrier calls which ensure that all\naccesses preceding setting of WORK_DONE_BIT are strictly ordered before\nsetting the flag. At the same time add a read barrier after reading of\nWORK_DONE_BIT in run_ordered_work which ensures all subsequent loads\nwould be strictly ordered after reading the bit. This in turn ensures\nare all accesses before WORK_DONE_BIT are going to be strictly ordered\nbefore any access that can occur in ordered_func.","publishedAt":"2024-04-10T18:56:28.194Z","updatedAt":"2026-08-05T08:46:35.936Z","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":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"bd660a20fea3ec60a49709ef5360f145ec0fe779","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"637d652d351fd4f263ef302dc52f3971d314e500","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"804a9d239ae9cbe88e861a7cd62319cc6ec7b136","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"ed058d735a70f4b063323f1a7bb33cda0f987513","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"670f6b3867c8f0f11e5097f353b164cecfec6179","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"6adbc07ebcaf8bead08b21687d49e0fc94400987","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"47e6f9f69153247109042010f3a77579e9dc61ff","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"45da9c1767ac31857df572f0a909fbe88fd5a7e9","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/async-thread.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.15","versionType":"semver"},{"version":"4.4.293","status":"unaffected","lessThanOrEqual":"4.4.*","versionType":"semver"},{"version":"4.9.291","status":"unaffected","lessThanOrEqual":"4.9.*","versionType":"semver"},{"version":"4.14.256","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.218","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.162","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.82","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.5","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"5.16","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/async-thread.c"]}],"references":["https://git.kernel.org/stable/c/bd660a20fea3ec60a49709ef5360f145ec0fe779","https://git.kernel.org/stable/c/637d652d351fd4f263ef302dc52f3971d314e500","https://git.kernel.org/stable/c/804a9d239ae9cbe88e861a7cd62319cc6ec7b136","https://git.kernel.org/stable/c/ed058d735a70f4b063323f1a7bb33cda0f987513","https://git.kernel.org/stable/c/670f6b3867c8f0f11e5097f353b164cecfec6179","https://git.kernel.org/stable/c/6adbc07ebcaf8bead08b21687d49e0fc94400987","https://git.kernel.org/stable/c/47e6f9f69153247109042010f3a77579e9dc61ff","https://git.kernel.org/stable/c/45da9c1767ac31857df572f0a909fbe88fd5a7e9"],"weaknesses":[],"ingestedAt":"2026-10-29T19:49:19.404Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2021/47xxx/CVE-2021-47189.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-47189","state":"PUBLISHED","datePublished":"2024-04-10T18:56:28.194Z","dateUpdated":"2026-08-05T08:46:35.936Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-03-25T09:12:14.113Z"},"containers":{"cna":{"title":"btrfs: fix memory ordering between normal and ordered work functions","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix memory ordering between normal and ordered work functions\n\nOrdered work functions aren't guaranteed to be handled by the same thread\nwhich executed the normal work functions. The only way execution between\nnormal/ordered functions is synchronized is via the WORK_DONE_BIT,\nunfortunately the used bitops don't guarantee any ordering whatsoever.\n\nThis manifested as seemingly inexplicable crashes on ARM64, where\nasync_chunk::inode is seen as non-null in async_cow_submit which causes\nsubmit_compressed_extents to be called and crash occurs because\nasync_chunk::inode suddenly became NULL. The call trace was similar to:\n\n    pc : submit_compressed_extents+0x38/0x3d0\n    lr : async_cow_submit+0x50/0xd0\n    sp : ffff800015d4bc20\n\n    <registers omitted for brevity>\n\n    Call trace:\n     submit_compressed_extents+0x38/0x3d0\n     async_cow_submit+0x50/0xd0\n     run_ordered_work+0xc8/0x280\n     btrfs_work_helper+0x98/0x250\n     process_one_work+0x1f0/0x4ac\n     worker_thread+0x188/0x504\n     kthread+0x110/0x114\n     ret_from_fork+0x10/0x18\n\nFix this by adding respective barrier calls which ensure that all\naccesses preceding setting of WORK_DONE_BIT are strictly ordered before\nsetting the flag. At the same time add a read barrier after reading of\nWORK_DONE_BIT in run_ordered_work which ensures all subsequent loads\nwould be strictly ordered after reading the bit. This in turn ensures\nare all accesses before WORK_DONE_BIT are going to be strictly ordered\nbefore any access that can occur in ordered_func."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"bd660a20fea3ec60a49709ef5360f145ec0fe779","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"637d652d351fd4f263ef302dc52f3971d314e500","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"804a9d239ae9cbe88e861a7cd62319cc6ec7b136","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"ed058d735a70f4b063323f1a7bb33cda0f987513","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"670f6b3867c8f0f11e5097f353b164cecfec6179","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"6adbc07ebcaf8bead08b21687d49e0fc94400987","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"47e6f9f69153247109042010f3a77579e9dc61ff","versionType":"git"},{"version":"08a9ff3264181986d1d692a4e6fce3669700c9f8","status":"affected","lessThan":"45da9c1767ac31857df572f0a909fbe88fd5a7e9","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/async-thread.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.15","versionType":"semver"},{"version":"4.4.293","status":"unaffected","lessThanOrEqual":"4.4.*","versionType":"semver"},{"version":"4.9.291","status":"unaffected","lessThanOrEqual":"4.9.*","versionType":"semver"},{"version":"4.14.256","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.218","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.162","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.82","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.5","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"5.16","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/async-thread.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/bd660a20fea3ec60a49709ef5360f145ec0fe779"},{"url":"https://git.kernel.org/stable/c/637d652d351fd4f263ef302dc52f3971d314e500"},{"url":"https://git.kernel.org/stable/c/804a9d239ae9cbe88e861a7cd62319cc6ec7b136"},{"url":"https://git.kernel.org/stable/c/ed058d735a70f4b063323f1a7bb33cda0f987513"},{"url":"https://git.kernel.org/stable/c/670f6b3867c8f0f11e5097f353b164cecfec6179"},{"url":"https://git.kernel.org/stable/c/6adbc07ebcaf8bead08b21687d49e0fc94400987"},{"url":"https://git.kernel.org/stable/c/47e6f9f69153247109042010f3a77579e9dc61ff"},{"url":"https://git.kernel.org/stable/c/45da9c1767ac31857df572f0a909fbe88fd5a7e9"}],"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 - The bug is in btrfs async workqueue ordering during local writeback (write/fsync → delalloc → cow_file_range_async / btrfs_wq_submit_bio), not in a network-facing protocol handler.\nAC:L - An attacker can create many concurrent compression/async bio work items so worker threads race on WORK_DONE_BIT visibility; this manifested under load on ARM64 without relying on conditions outside attacker influence.\nPR:L - An unprivileged user with write access to a mounted btrfs (e.g. home directory) can trigger the path, and can enable per-file compression via chattr/FS_IOC_SETFLAGS on files they own.\nUI:N - The attacker triggers writeback themselves via ordinary writes/fsync; no separate victim action is required.\nS:U - Impact stays within the host kernel privilege boundary; this is not a VM/IOMMU/sandbox escape.\nC:H - Missing barriers allow ordered_func to observe torn producer state (extent lists, page pointer arrays, bio/csum fields), which can yield wild/stale pointer use and arbitrary kernel memory disclosure.\nI:H - The same torn shared state can drive submit paths with inconsistent pointers/metadata (compressed extent submission or async bio mapping), enabling memory corruption and integrity compromise beyond a clean crash.\nA:H - The bug causes kernel NULL dereferences and oops/hangs in async_cow_submit/submit_compressed_extents, as seen on ARM64."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T08:46:35.936Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.15","versionEndExcluding":"4.4.293"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.15","versionEndExcluding":"4.9.291"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.15","versionEndExcluding":"4.14.256"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.15","versionEndExcluding":"4.19.218"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.15","versionEndExcluding":"5.4.162"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.15","versionEndExcluding":"5.10.82"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.15","versionEndExcluding":"5.15.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.15","versionEndExcluding":"5.16"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"cvssV3_1":{"scope":"UNCHANGED","version":"3.1","baseScore":6.3,"attackVector":"NETWORK","baseSeverity":"MEDIUM","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L","integrityImpact":"LOW","userInteraction":"NONE","attackComplexity":"LOW","availabilityImpact":"LOW","privilegesRequired":"LOW","confidentialityImpact":"LOW"}},{"other":{"type":"ssvc","content":{"timestamp":"2024-04-10T19:44:25.164224Z","id":"CVE-2021-47189","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"problemTypes":[{"descriptions":[{"type":"CWE","lang":"en","description":"CWE-noinfo Not enough information"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2024-11-01T17:56:06.717Z"}},{"title":"CVE Program Container","references":[{"url":"https://git.kernel.org/stable/c/bd660a20fea3ec60a49709ef5360f145ec0fe779","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/637d652d351fd4f263ef302dc52f3971d314e500","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/804a9d239ae9cbe88e861a7cd62319cc6ec7b136","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/ed058d735a70f4b063323f1a7bb33cda0f987513","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/670f6b3867c8f0f11e5097f353b164cecfec6179","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/6adbc07ebcaf8bead08b21687d49e0fc94400987","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/47e6f9f69153247109042010f3a77579e9dc61ff","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/45da9c1767ac31857df572f0a909fbe88fd5a7e9","tags":["x_transferred"]}],"providerMetadata":{"shortName":"CVE","orgId":"af854a3a-2127-422b-91ae-364da2661108","dateUpdated":"2024-08-04T05:32:07.308Z"}}]}}}