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CVE-2021-47646 (GCVE-0-2021-47646)

Vulnerability from cvelistv5 – Published: 2025-02-26 01:54 – Updated: 2026-08-11 02:05
VLAI
Title
Revert "Revert "block, bfq: honor already-setup queue merges""
Summary
In the Linux kernel, the following vulnerability has been resolved: Revert "Revert "block, bfq: honor already-setup queue merges"" A crash [1] happened to be triggered in conjunction with commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges"). The latter was then reverted by commit ebc69e897e17 ("Revert "block, bfq: honor already-setup queue merges""). Yet, the reverted commit was not the one introducing the bug. In fact, it actually triggered a UAF introduced by a different commit, and now fixed by commit d29bd41428cf ("block, bfq: reset last_bfqq_created on group change"). So, there is no point in keeping commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges") out. This commit restores it. [1] https://bugzilla.kernel.org/show_bug.cgi?id=214503
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-02-27 17:59 UTC
CWE
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 430a67f9d6169a7b3e328bceb2ef9542e4153c7c , < 65d8a737452e88f251fe5d925371de6d606df613 (git)
Affected: 430a67f9d6169a7b3e328bceb2ef9542e4153c7c , < abc2129e646af7b43025d90a071f83043f1ae76c (git)
Affected: 430a67f9d6169a7b3e328bceb2ef9542e4153c7c , < 4083925bd6dc89216d156474a8076feec904e607 (git)
Affected: 430a67f9d6169a7b3e328bceb2ef9542e4153c7c , < 15729ff8143f8135b03988a100a19e66d7cb7ecd (git)
guessed Create a notification for this product.
Linux Linux Affected: 5.13
Unaffected: 0 , < 5.13 (semver)
Unaffected: 5.15.33 , ≤ 5.15.* (semver)
Unaffected: 5.16.19 , ≤ 5.16.* (semver)
Unaffected: 5.17.2 , ≤ 5.17.* (semver)
Unaffected: 5.18 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
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In fact, it actually triggered a UAF\\nintroduced by a different commit, and now fixed by commit d29bd41428cf\\n(\\\"block, bfq: reset last_bfqq_created on group change\\\").\\n\\nSo, there is no point in keeping commit 2d52c58b9c9b (\\\"block, bfq:\\nhonor already-setup queue merges\\\") out. This commit restores it.\\n\\n[1] https://bugzilla.kernel.org/show_bug.cgi?id=214503\"},{\"lang\":\"es\",\"value\":\"En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: Revert \\\"Revert \\\"block, bfq: respetar las fusiones de colas ya configuradas\\\"\\\" Se produjo un fallo [1] junto con la confirmaci\u00f3n 2d52c58b9c9b (\\\"block, bfq: respetar las fusiones de colas ya configuradas\\\"). Esta \u00faltima se revirti\u00f3 mediante la confirmaci\u00f3n ebc69e897e17 (\\\"Revert \\\"block, bfq: respetar las fusiones de colas ya configuradas\\\"\\\"). Sin embargo, la confirmaci\u00f3n revertida no fue la que introdujo el error. De hecho, activ\u00f3 una UAF introducida por una confirmaci\u00f3n diferente, y ahora corregida por la confirmaci\u00f3n d29bd41428cf (\\\"block, bfq: restablecer last_bfqq_created al cambiar de grupo\\\"). Por lo tanto, no tiene sentido mantener la confirmaci\u00f3n 2d52c58b9c9b (\\\"block, bfq: respetar las fusiones de colas ya configuradas\\\"). Esta confirmaci\u00f3n la restaura. 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      "source": "Red Hat CSAF VEX",
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      "title": "kernel: Revert \"Revert \"block, bfq: honor already-setup queue merges\"\"",
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    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"cvssV3_1\": {\"scope\": \"UNCHANGED\", \"version\": \"3.1\", \"baseScore\": 7.8, \"attackVector\": \"LOCAL\", \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H\", \"integrityImpact\": \"HIGH\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"LOW\", \"availabilityImpact\": \"HIGH\", \"privilegesRequired\": \"LOW\", \"confidentialityImpact\": \"HIGH\"}}, {\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2021-47646\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"total\"}], \"version\": \"2.0.3\", \"timestamp\": \"2025-02-27T17:59:39.194997Z\"}}}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-416\", \"description\": \"CWE-416 Use After Free\"}]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2025-02-27T17:59:40.880Z\"}}], \"cna\": {\"title\": \"Revert \\\"Revert \\\"block, bfq: honor already-setup queue merges\\\"\\\"\", \"metrics\": [{\"cvssV3_1\": {\"version\": \"3.1\", \"baseScore\": 7.8, \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"AV:L - The vulnerability is in the BFQ block I/O scheduler and is reached via local syscalls that submit I/O (read/write/fsync/ioctl), through bfq_init_rq \\u2192 bfq_get_queue / bfq_setup_cooperator; it is not reachable from network packet processing.\\nAC:L - An unprivileged attacker can reliably drive the buggy path by spawning processes that issue concurrent I/O and by migrating between blkcgs so queues are created, merged, moved, and freed under attacker control; success does not depend on victim state beyond BFQ being the active scheduler.\\nPR:L - Only an unprivileged local account is required to submit I/O on a BFQ-scheduled device; changing the elevator needs privileges, but BFQ (with group I/O scheduling) is a common/default deployment (e.g. Android), so the attacker need not already be root.\\nUI:N - Exploitation requires no action by another user; the attacker triggers the bug solely through their own I/O and process/cgroup activity.\\nS:U - Impact is confined to the local kernel\u0027s security authority (memory corruption / privilege escalation on the host); there is no VM escape, IOMMU bypass, or other cross-boundary scope change.\\nC:H - The issue is a use-after-free of bfq_queue objects (dangling last_bfqq_created / broken merge state), which per kernel CVSS guidance yields an arbitrary-read primitive via heap reuse of the freed object.\\nI:H - The same UAF/memory-corruption condition enables heap spraying and arbitrary-write / control-flow hijacking in kernel context, so integrity impact is High.\\nA:H - The bug causes kernel oops/BUG_ON and slab freelist corruption (demonstrated in bugzilla 214503 crashes in bfq_get_queue / bfq_do_early_stable_merge), so availability impact is High.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"430a67f9d6169a7b3e328bceb2ef9542e4153c7c\", \"lessThan\": \"65d8a737452e88f251fe5d925371de6d606df613\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"430a67f9d6169a7b3e328bceb2ef9542e4153c7c\", \"lessThan\": \"abc2129e646af7b43025d90a071f83043f1ae76c\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"430a67f9d6169a7b3e328bceb2ef9542e4153c7c\", \"lessThan\": \"4083925bd6dc89216d156474a8076feec904e607\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"430a67f9d6169a7b3e328bceb2ef9542e4153c7c\", \"lessThan\": \"15729ff8143f8135b03988a100a19e66d7cb7ecd\", \"versionType\": \"git\"}], \"programFiles\": [\"block/bfq-iosched.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"5.13\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"5.13\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.15.33\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"5.16.19\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.16.*\"}, {\"status\": \"unaffected\", \"version\": \"5.17.2\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.17.*\"}, {\"status\": \"unaffected\", \"version\": \"5.18\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"block/bfq-iosched.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/65d8a737452e88f251fe5d925371de6d606df613\"}, {\"url\": \"https://git.kernel.org/stable/c/abc2129e646af7b43025d90a071f83043f1ae76c\"}, {\"url\": \"https://git.kernel.org/stable/c/4083925bd6dc89216d156474a8076feec904e607\"}, {\"url\": \"https://git.kernel.org/stable/c/15729ff8143f8135b03988a100a19e66d7cb7ecd\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nRevert \\\"Revert \\\"block, bfq: honor already-setup queue merges\\\"\\\"\\n\\nA crash [1] happened to be triggered in conjunction with commit\\n2d52c58b9c9b (\\\"block, bfq: honor already-setup queue merges\\\"). The\\nlatter was then reverted by commit ebc69e897e17 (\\\"Revert \\\"block, bfq:\\nhonor already-setup queue merges\\\"\\\"). Yet, the reverted commit was not\\nthe one introducing the bug. In fact, it actually triggered a UAF\\nintroduced by a different commit, and now fixed by commit d29bd41428cf\\n(\\\"block, bfq: reset last_bfqq_created on group change\\\").\\n\\nSo, there is no point in keeping commit 2d52c58b9c9b (\\\"block, bfq:\\nhonor already-setup queue merges\\\") out. This commit restores it.\\n\\n[1] https://bugzilla.kernel.org/show_bug.cgi?id=214503\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.33\", \"versionStartIncluding\": \"5.13\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.16.19\", \"versionStartIncluding\": \"5.13\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.17.2\", \"versionStartIncluding\": \"5.13\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.18\", \"versionStartIncluding\": \"5.13\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-11T02:05:32.009Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2021-47646\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-11T02:05:32.009Z\", \"dateReserved\": \"2025-02-26T01:48:21.520Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2025-02-26T01:54:15.122Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
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}