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CVE-2021-47044— sched/fair: Fix shift-out-of-bounds in load_balance()

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel 存在安全漏洞，该漏洞源于 load_balance() 方法中存在移位越界问题。

AI Predicted 5.5 Difficulty: Moderate EPSS 0.27% · P17

Possible ATT&CK Techniques 1 AI

T1068 · Exploitation for Privilege Escalation

Affected Version Matrix 10

VendorProduct Version RangeStatus
Linux Linux 5a7f555904671c0737819fe4d19bd6143de3f6c0< 80862cbf76c2646f709a57c4517aefe0b094c774 affected
5a7f555904671c0737819fe4d19bd6143de3f6c0< 2f3eab368e313dba35fc2f51ede778bf7b030b54 affected
5a7f555904671c0737819fe4d19bd6143de3f6c0< 805cea93e66ca7deaaf6ad3b67224ce47c104c2f affected
5a7f555904671c0737819fe4d19bd6143de3f6c0< 39a2a6eb5c9b66ea7c8055026303b3aa681b49a5 affected
5.10 affected
< 5.10 unaffected
5.10.37≤ 5.10.* unaffected
5.11.21≤ 5.11.* unaffected
… +2 more rows
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I. Basic Information for CVE-2021-47044

Vulnerability Information
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Vulnerability Title
sched/fair: Fix shift-out-of-bounds in load_balance()
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: sched/fair: Fix shift-out-of-bounds in load_balance() Syzbot reported a handful of occurrences where an sd->nr_balance_failed can grow to much higher values than one would expect. A successful load_balance() resets it to 0; a failed one increments it. Once it gets to sd->cache_nice_tries + 3, this *should* trigger an active balance, which will either set it to sd->cache_nice_tries+1 or reset it to 0. However, in case the to-be-active-balanced task is not allowed to run on env->dst_cpu, then the increment is done without any further modification. This could then be repeated ad nauseam, and would explain the absurdly high values reported by syzbot (86, 149). VincentG noted there is value in letting sd->cache_nice_tries grow, so the shift itself should be fixed. That means preventing: """ If the value of the right operand is negative or is greater than or equal to the width of the promoted left operand, the behavior is undefined. """ Thus we need to cap the shift exponent to BITS_PER_TYPE(typeof(lefthand)) - 1. I had a look around for other similar cases via coccinelle: @expr@ position pos; expression E1; expression E2; @@ ( E1 >> E2@pos | E1 >> E2@pos ) @cst depends on expr@ position pos; expression expr.E1; constant cst; @@ ( E1 >> cst@pos | E1 << cst@pos ) @script:python depends on !cst@ pos << expr.pos; exp << expr.E2; @@ # Dirty hack to ignore constexpr if exp.upper() != exp: coccilib.report.print_report(pos[0], "Possible UB shift here") The only other match in kernel/sched is rq_clock_thermal() which employs sched_thermal_decay_shift, and that exponent is already capped to 10, so that one is fine.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel 存在安全漏洞，该漏洞源于 load_balance() 方法中存在移位越界问题。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 5a7f555904671c0737819fe4d19bd6143de3f6c0 ~ 80862cbf76c2646f709a57c4517aefe0b094c774 -
Linux Linux 5.10 -

II. Public POCs for CVE-2021-47044

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III. Intelligence Information for CVE-2021-47044

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Other References for CVE-2021-47044 (3)

Same Patch Batch · Linux · 2024-02-28 · 86 CVEs total

CVE-2021-47036 9.8 CRITICAL udp: skip L4 aggregation for UDP tunnel packets
CVE-2021-46999 9.8 CRITICAL sctp: do asoc update earlier in sctp_sf_do_dupcook_a
CVE-2021-47013 9.8 CRITICAL net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send
CVE-2021-47035 8.8 HIGH iommu/vt-d: Remove WO permissions on second-level paging entries
CVE-2021-47017 8.8 HIGH ath10k: Fix a use after free in ath10k_htc_send_bundle
CVE-2021-47049 8.4 HIGH Drivers: hv: vmbus: Use after free in __vmbus_open()
CVE-2021-47014 7.8 HIGH net/sched: act_ct: fix wild memory access when clearing fragments
CVE-2021-46984 7.8 HIGH kyber: fix out of bounds access when preempted
CVE-2021-46998 7.8 HIGH ethernet:enic: Fix a use after free bug in enic_hard_start_xmit
CVE-2021-47048 7.8 HIGH spi: spi-zynqmp-gqspi: fix use-after-free in zynqmp_qspi_exec_op
CVE-2021-46992 7.8 HIGH netfilter: nftables: avoid overflows in nft_hash_buckets()
CVE-2021-47012 7.8 HIGH RDMA/siw: Fix a use after free in siw_alloc_mr
CVE-2021-47011 7.8 HIGH mm: memcontrol: slab: fix obtain a reference to a freeing memcg
CVE-2021-47040 7.8 HIGH io_uring: fix overflows checks in provide buffers
CVE-2020-36787 7.8 HIGH media: aspeed: fix clock handling logic
CVE-2021-46977 7.8 HIGH KVM: VMX: Disable preemption when probing user return MSRs
CVE-2021-46993 7.8 HIGH sched: Fix out-of-bound access in uclamp
CVE-2020-36785 7.8 HIGH media: atomisp: Fix use after free in atomisp_alloc_css_stat_bufs()
CVE-2021-46983 7.5 HIGH nvmet-rdma: Fix NULL deref when SEND is completed with error
CVE-2021-47041 7.5 HIGH nvmet-tcp: fix incorrect locking in state_change sk callback

Showing top 20 of 86 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2021-47044

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