CVE-2021-46989 (GCVE-0-2021-46989)
Vulnerability from cvelistv5
Published
2024-02-28 08:13
Modified
2026-08-05 08:45
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
hfsplus: prevent corruption in shrinking truncate
I believe there are some issues introduced by commit 31651c607151
("hfsplus: avoid deadlock on file truncation")
HFS+ has extent records which always contains 8 extents. In case the
first extent record in catalog file gets full, new ones are allocated from
extents overflow file.
In case shrinking truncate happens to middle of an extent record which
locates in extents overflow file, the logic in hfsplus_file_truncate() was
changed so that call to hfs_brec_remove() is not guarded any more.
Right action would be just freeing the extents that exceed the new size
inside extent record by calling hfsplus_free_extents(), and then check if
the whole extent record should be removed. However since the guard
(blk_cnt > start) is now after the call to hfs_brec_remove(), this has
unfortunate effect that the last matching extent record is removed
unconditionally.
To reproduce this issue, create a file which has at least 10 extents, and
then perform shrinking truncate into middle of the last extent record, so
that the number of remaining extents is not under or divisible by 8. This
causes the last extent record (8 extents) to be removed totally instead of
truncating into middle of it. Thus this causes corruption, and lost data.
Fix for this is simply checking if the new truncated end is below the
start of this extent record, making it safe to remove the full extent
record. However call to hfs_brec_remove() can't be moved to it's previous
place since we're dropping ->tree_lock and it can cause a race condition
and the cached info being invalidated possibly corrupting the node data.
Another issue is related to this one. When entering into the block
(blk_cnt > start) we are not holding the ->tree_lock. We break out from
the loop not holding the lock, but hfs_find_exit() does unlock it. Not
sure if it's possible for someone else to take the lock under our feet,
but it can cause hard to debug errors and premature unlocking. Even if
there's no real risk of it, the locking should still always be kept in
balance. Thus taking the lock now just before the check.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: 31651c607151f1034cfb57e5a78678bea54c362b Version: 31651c607151f1034cfb57e5a78678bea54c362b Version: 31651c607151f1034cfb57e5a78678bea54c362b Version: 31651c607151f1034cfb57e5a78678bea54c362b Version: 31651c607151f1034cfb57e5a78678bea54c362b Version: 31651c607151f1034cfb57e5a78678bea54c362b |
||
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the same path can also unlock tree_lock while another inode\\u2019s extent ops hold it, enabling concurrent btree modification.\\nA:H - Breaking out of the truncate loop without re-acquiring tree_lock causes hfs_find_exit() to mutex_unlock an already-unlocked lock (kernel WARN/oops or hang under contention), and the resulting filesystem corruption denies access to affected data/volume.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"31651c607151f1034cfb57e5a78678bea54c362b\", \"lessThan\": \"52dde855663e5db824af51db39b5757d2ef3e28a\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"31651c607151f1034cfb57e5a78678bea54c362b\", \"lessThan\": \"c451a6bafb5f422197d31536f82116aed132b72c\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"31651c607151f1034cfb57e5a78678bea54c362b\", \"lessThan\": \"adbd8a2a8cc05d9e501f93e5c95c59307874cc99\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"31651c607151f1034cfb57e5a78678bea54c362b\", \"lessThan\": \"c477f62db1a0c0ecaa60a29713006ceeeb04b685\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"31651c607151f1034cfb57e5a78678bea54c362b\", \"lessThan\": \"97314e45aa1223a42d60256a62c5d9af54baf446\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"31651c607151f1034cfb57e5a78678bea54c362b\", \"lessThan\": \"c3187cf32216313fb316084efac4dab3a8459b1d\", \"versionType\": \"git\"}], \"programFiles\": [\"fs/hfsplus/extents.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"4.19\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"4.19\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"4.19.191\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"4.19.*\"}, {\"status\": \"unaffected\", \"version\": \"5.4.120\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.4.*\"}, {\"status\": \"unaffected\", \"version\": \"5.10.38\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.11.22\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.11.*\"}, {\"status\": \"unaffected\", \"version\": \"5.12.5\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.12.*\"}, {\"status\": \"unaffected\", \"version\": \"5.13\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"fs/hfsplus/extents.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/52dde855663e5db824af51db39b5757d2ef3e28a\"}, {\"url\": \"https://git.kernel.org/stable/c/c451a6bafb5f422197d31536f82116aed132b72c\"}, {\"url\": \"https://git.kernel.org/stable/c/adbd8a2a8cc05d9e501f93e5c95c59307874cc99\"}, {\"url\": \"https://git.kernel.org/stable/c/c477f62db1a0c0ecaa60a29713006ceeeb04b685\"}, {\"url\": \"https://git.kernel.org/stable/c/97314e45aa1223a42d60256a62c5d9af54baf446\"}, {\"url\": \"https://git.kernel.org/stable/c/c3187cf32216313fb316084efac4dab3a8459b1d\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nhfsplus: prevent corruption in shrinking truncate\\n\\nI believe there are some issues introduced by commit 31651c607151\\n(\\\"hfsplus: avoid deadlock on file truncation\\\")\\n\\nHFS+ has extent records which always contains 8 extents. In case the\\nfirst extent record in catalog file gets full, new ones are allocated from\\nextents overflow file.\\n\\nIn case shrinking truncate happens to middle of an extent record which\\nlocates in extents overflow file, the logic in hfsplus_file_truncate() was\\nchanged so that call to hfs_brec_remove() is not guarded any more.\\n\\nRight action would be just freeing the extents that exceed the new size\\ninside extent record by calling hfsplus_free_extents(), and then check if\\nthe whole extent record should be removed. However since the guard\\n(blk_cnt \u003e start) is now after the call to hfs_brec_remove(), this has\\nunfortunate effect that the last matching extent record is removed\\nunconditionally.\\n\\nTo reproduce this issue, create a file which has at least 10 extents, and\\nthen perform shrinking truncate into middle of the last extent record, so\\nthat the number of remaining extents is not under or divisible by 8. This\\ncauses the last extent record (8 extents) to be removed totally instead of\\ntruncating into middle of it. Thus this causes corruption, and lost data.\\n\\nFix for this is simply checking if the new truncated end is below the\\nstart of this extent record, making it safe to remove the full extent\\nrecord. However call to hfs_brec_remove() can\u0027t be moved to it\u0027s previous\\nplace since we\u0027re dropping -\u003etree_lock and it can cause a race condition\\nand the cached info being invalidated possibly corrupting the node data.\\n\\nAnother issue is related to this one. When entering into the block\\n(blk_cnt \u003e start) we are not holding the -\u003etree_lock. We break out from\\nthe loop not holding the lock, but hfs_find_exit() does unlock it. Not\\nsure if it\u0027s possible for someone else to take the lock under our feet,\\nbut it can cause hard to debug errors and premature unlocking. Even if\\nthere\u0027s no real risk of it, the locking should still always be kept in\\nbalance. Thus taking the lock now just before the check.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"4.19.191\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.4.120\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.38\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.11.22\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.12.5\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.13\", \"versionStartIncluding\": \"4.19\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T08:45:24.640Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2021-46989\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-05T08:45:24.640Z\", \"dateReserved\": \"2024-02-27T18:42:55.948Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-02-28T08:13:15.930Z\", \"assignerShortName\": \"Linux\"}",
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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