{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2021-46984", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2024-02-27T18:42:55.946Z", "datePublished": "2024-02-28T08:13:12.835Z", "dateUpdated": "2026-08-05T08:45:23.565Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T08:45:23.565Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nkyber: fix out of bounds access when preempted\n\n__blk_mq_sched_bio_merge() gets the ctx and hctx for the current CPU and\npasses the hctx to ->bio_merge(). kyber_bio_merge() then gets the ctx\nfor the current CPU again and uses that to get the corresponding Kyber\ncontext in the passed hctx. However, the thread may be preempted between\nthe two calls to blk_mq_get_ctx(), and the ctx returned the second time\nmay no longer correspond to the passed hctx. This \"works\" accidentally\nmost of the time, but it can cause us to read garbage if the second ctx\ncame from an hctx with more ctx's than the first one (i.e., if\nctx->index_hw[hctx->type] > hctx->nr_ctx).\n\nThis manifested as this UBSAN array index out of bounds error reported\nby Jakub:\n\nUBSAN: array-index-out-of-bounds in ../kernel/locking/qspinlock.c:130:9\nindex 13106 is out of range for type 'long unsigned int [128]'\nCall Trace:\n dump_stack+0xa4/0xe5\n ubsan_epilogue+0x5/0x40\n __ubsan_handle_out_of_bounds.cold.13+0x2a/0x34\n queued_spin_lock_slowpath+0x476/0x480\n do_raw_spin_lock+0x1c2/0x1d0\n kyber_bio_merge+0x112/0x180\n blk_mq_submit_bio+0x1f5/0x1100\n submit_bio_noacct+0x7b0/0x870\n submit_bio+0xc2/0x3a0\n btrfs_map_bio+0x4f0/0x9d0\n btrfs_submit_data_bio+0x24e/0x310\n submit_one_bio+0x7f/0xb0\n submit_extent_page+0xc4/0x440\n __extent_writepage_io+0x2b8/0x5e0\n __extent_writepage+0x28d/0x6e0\n extent_write_cache_pages+0x4d7/0x7a0\n extent_writepages+0xa2/0x110\n do_writepages+0x8f/0x180\n __writeback_single_inode+0x99/0x7f0\n writeback_sb_inodes+0x34e/0x790\n __writeback_inodes_wb+0x9e/0x120\n wb_writeback+0x4d2/0x660\n wb_workfn+0x64d/0xa10\n process_one_work+0x53a/0xa80\n worker_thread+0x69/0x5b0\n kthread+0x20b/0x240\n ret_from_fork+0x1f/0x30\n\nOnly Kyber uses the hctx, so fix it by passing the request_queue to\n->bio_merge() instead. BFQ and mq-deadline just use that, and Kyber can\nmap the queues itself to avoid the mismatch." } ], "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 vulnerability is in the Kyber block I/O scheduler on the local bio submit path (write/read → submit_bio → blk_mq_submit_bio → kyber_bio_merge), so exploitation requires local process access to issue I/O, not a network protocol handler.\nAC:L - An attacker controls I/O submission and can amplify the CPU-migration race via affinity bouncing, concurrent writers, and load; the race has occurred under real I/O pressure, so success does not depend on conditions beyond attacker influence.\nPR:L - Any unprivileged local user who can read/write files on a device using Kyber reaches the vulnerable merge path with no capabilities required; selecting Kyber via sysfs needs root but is a deployment precondition, not an attacker privilege.\nUI:N - Exploitation only requires the attacker’s own I/O syscalls; no separate victim action such as mounting a filesystem or opening a crafted file is needed.\nS:U - Impact is memory corruption within the host kernel’s block layer and does not cross a VM, IOMMU, or other distinct security authority boundary.\nC:H - The OOB index reads an out-of-range kyber_ctx_queue (lock and list heads) from adjacent heap memory, and the subsequent list walk dereferences those attacker-influenceable request pointers, enabling arbitrary kernel memory disclosure.\nI:H - spin_lock on the OOB object writes a corrupted lock word, and blk_bio_list_merge can mutate poisoned list pointers, yielding classic linked-list memory corruption suitable for arbitrary write and control-flow hijacking.\nA:H - Locking and walking garbage kyber_ctx_queue state causes kernel oops/panic (as in the reported qspinlock UBSAN failure in kyber_bio_merge), so availability impact is complete." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "block/bfq-iosched.c", "block/blk-mq-sched.c", "block/kyber-iosched.c", "block/mq-deadline.c", "include/linux/elevator.h" ], "versions": [ { "version": "a6088845c2bf754d6cb2572b484180680b037804", "lessThan": "0b6b4b90b74c27bea968c214d820ba4254b903a5", "status": "affected", "versionType": "git" }, { "version": "a6088845c2bf754d6cb2572b484180680b037804", "lessThan": "54dbe2d2c1fcabf650c7a8b747601da355cd7f9f", "status": "affected", "versionType": "git" }, { "version": "a6088845c2bf754d6cb2572b484180680b037804", "lessThan": "a287cd84e047045f5a4d4da793414e848de627c6", "status": "affected", "versionType": "git" }, { "version": "a6088845c2bf754d6cb2572b484180680b037804", "lessThan": "2ef3c76540c49167a0bc3d5f80d00fd1fc4586df", "status": "affected", "versionType": "git" }, { "version": "a6088845c2bf754d6cb2572b484180680b037804", "lessThan": "efed9a3337e341bd0989161b97453b52567bc59d", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "block/bfq-iosched.c", "block/blk-mq-sched.c", "block/kyber-iosched.c", "block/mq-deadline.c", "include/linux/elevator.h" ], "versions": [ { "version": "4.18", "status": "affected" }, { "version": "0", "lessThan": "4.18", "status": "unaffected", "versionType": "semver" }, { "version": "5.4.120", "lessThanOrEqual": "5.4.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.38", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.11.22", "lessThanOrEqual": "5.11.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.12.5", "lessThanOrEqual": "5.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.13", "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": "4.18", "versionEndExcluding": "5.4.120" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.18", "versionEndExcluding": "5.10.38" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.18", "versionEndExcluding": "5.11.22" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.18", "versionEndExcluding": "5.12.5" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.18", "versionEndExcluding": "5.13" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/0b6b4b90b74c27bea968c214d820ba4254b903a5" }, { "url": "https://git.kernel.org/stable/c/54dbe2d2c1fcabf650c7a8b747601da355cd7f9f" }, { "url": "https://git.kernel.org/stable/c/a287cd84e047045f5a4d4da793414e848de627c6" }, { "url": "https://git.kernel.org/stable/c/2ef3c76540c49167a0bc3d5f80d00fd1fc4586df" }, { "url": "https://git.kernel.org/stable/c/efed9a3337e341bd0989161b97453b52567bc59d" } ], "title": "kyber: fix out of bounds access when preempted", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "providerMetadata": { "orgId": "af854a3a-2127-422b-91ae-364da2661108", "shortName": "CVE", "dateUpdated": "2024-08-04T05:24:37.898Z" }, "title": "CVE Program Container", "references": [ { "url": "https://git.kernel.org/stable/c/0b6b4b90b74c27bea968c214d820ba4254b903a5", "tags": [ "x_transferred" ] }, { "url": "https://git.kernel.org/stable/c/54dbe2d2c1fcabf650c7a8b747601da355cd7f9f", "tags": [ "x_transferred" ] }, { "url": "https://git.kernel.org/stable/c/a287cd84e047045f5a4d4da793414e848de627c6", "tags": [ "x_transferred" ] }, { "url": "https://git.kernel.org/stable/c/2ef3c76540c49167a0bc3d5f80d00fd1fc4586df", "tags": [ "x_transferred" ] }, { "url": "https://git.kernel.org/stable/c/efed9a3337e341bd0989161b97453b52567bc59d", "tags": [ "x_transferred" ] } ] }, { "metrics": [ { "other": { "type": "ssvc", "content": { "id": "CVE-2021-46984", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "no" }, { "Technical Impact": "partial" } ], "version": "2.0.3", "timestamp": "2024-09-10T16:01:11.596982Z" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2024-09-11T17:33:40.792Z" } } ] } }