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CVE-2021-46921— locking/qrwlock: Fix ordering in queued_write_lock_slowpath()

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，该漏洞源于虽然此代码是在持有 wait_lock 的情况下执行的，但读者无需持有 wait_lock 即可获取锁。

CVSS 7.8 · High EPSS 0.24% · P14

Possible ATT&CK Techniques 1 AI

T1068 · Exploitation for Privilege Escalation

Affected Version Matrix 12

VendorProduct Version RangeStatus
Linux Linux b519b56e378ee82caf9b079b04f5db87dedc3251< 5902f9453a313be8fe78cbd7e7ca9dba9319fc6e affected
b519b56e378ee82caf9b079b04f5db87dedc3251< 82808cc026811fbc3ecf0c0b267a12a339eead56 affected
b519b56e378ee82caf9b079b04f5db87dedc3251< 82fa9ced35d88581cffa4a1c856fc41fca96d80a affected
b519b56e378ee82caf9b079b04f5db87dedc3251< d558fcdb17139728347bccc60a16af3e639649d2 affected
b519b56e378ee82caf9b079b04f5db87dedc3251< 84a24bf8c52e66b7ac89ada5e3cfbe72d65c1896 affected
4.15 affected
< 4.15 unaffected
4.19.189≤ 4.19.* unaffected
… +4 more rows
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I. Basic Information for CVE-2021-46921

Vulnerability Information
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Vulnerability Title
locking/qrwlock: Fix ordering in queued_write_lock_slowpath()
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: locking/qrwlock: Fix ordering in queued_write_lock_slowpath() While this code is executed with the wait_lock held, a reader can acquire the lock without holding wait_lock. The writer side loops checking the value with the atomic_cond_read_acquire(), but only truly acquires the lock when the compare-and-exchange is completed successfully which isn’t ordered. This exposes the window between the acquire and the cmpxchg to an A-B-A problem which allows reads following the lock acquisition to observe values speculatively before the write lock is truly acquired. We've seen a problem in epoll where the reader does a xchg while holding the read lock, but the writer can see a value change out from under it. Writer | Reader -------------------------------------------------------------------------------- ep_scan_ready_list() | |- write_lock_irq() | |- queued_write_lock_slowpath() | |- atomic_cond_read_acquire() | | read_lock_irqsave(&ep->lock, flags); --> (observes value before unlock) | chain_epi_lockless() | | epi->next = xchg(&ep->ovflist, epi); | | read_unlock_irqrestore(&ep->lock, flags); | | | atomic_cmpxchg_relaxed() | |-- READ_ONCE(ep->ovflist); | A core can order the read of the ovflist ahead of the atomic_cmpxchg_relaxed(). Switching the cmpxchg to use acquire semantics addresses this issue at which point the atomic_cond_read can be switched to use relaxed semantics. [peterz: use try_cmpxchg()]
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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，该漏洞源于虽然此代码是在持有 wait_lock 的情况下执行的，但读者无需持有 wait_lock 即可获取锁。
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 b519b56e378ee82caf9b079b04f5db87dedc3251 ~ 5902f9453a313be8fe78cbd7e7ca9dba9319fc6e -
Linux Linux 4.15 -

II. Public POCs for CVE-2021-46921

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III. Intelligence Information for CVE-2021-46921

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Other References for CVE-2021-46921 (5)

Same Patch Batch · Linux · 2024-02-27 · 67 CVEs total

CVE-2021-46911 9.8 CRITICAL ch_ktls: Fix kernel panic
CVE-2021-46955 8.2 HIGH openvswitch: fix stack OOB read while fragmenting IPv4 packets
CVE-2021-46936 7.8 HIGH net: fix use-after-free in tw_timer_handler
CVE-2021-46969 7.8 HIGH bus: mhi: core: Fix invalid error returning in mhi_queue
CVE-2021-46973 7.8 HIGH net: qrtr: Avoid potential use after free in MHI send
CVE-2021-46913 7.8 HIGH netfilter: nftables: clone set element expression template
CVE-2021-46967 7.8 HIGH vhost-vdpa: fix vm_flags for virtqueue doorbell mapping
CVE-2021-46925 7.8 HIGH net/smc: fix kernel panic caused by race of smc_sock
CVE-2021-46963 7.8 HIGH scsi: qla2xxx: Fix crash in qla2xxx_mqueuecommand()
CVE-2021-46929 7.8 HIGH sctp: use call_rcu to free endpoint
CVE-2021-46958 7.8 HIGH btrfs: fix race between transaction aborts and fsyncs leading to use-after-free
CVE-2021-46933 7.8 HIGH usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.
CVE-2021-46922 7.8 HIGH KEYS: trusted: Fix TPM reservation for seal/unseal
CVE-2021-46960 7.5 HIGH cifs: Return correct error code from smb2_get_enc_key
CVE-2021-46948 7.5 HIGH sfc: farch: fix TX queue lookup in TX event handling
CVE-2021-46912 7.3 HIGH net: Make tcp_allowed_congestion_control readonly in non-init netns
CVE-2021-46974 7.1 HIGH bpf: Fix masking negation logic upon negative dst register
CVE-2021-46908 7.1 HIGH bpf: Use correct permission flag for mixed signed bounds arithmetic
CVE-2021-46910 7.0 HIGH ARM: 9063/1: mm: reduce maximum number of CPUs if DEBUG_KMAP_LOCAL is enabled
CVE-2021-46954 net/sched: sch_frag: fix stack OOB read while fragmenting IPv4 packets

Showing top 20 of 67 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2021-46921

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