CVE-2021-46921
"Linux kernel QRWLock Atomic A-B-A 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()]
INFO
Published Date :
Feb. 27, 2024, 10:15 a.m.
Last Modified :
April 10, 2024, 1:39 p.m.
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Remotely Exploitable :
No
Impact Score :
3.6
Exploitability Score :
1.8
References to Advisories, Solutions, and Tools
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information, practical solutions, and valuable tools related to
CVE-2021-46921
.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
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The following list is the news that have been mention
CVE-2021-46921
vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2021-46921
vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
May. 28, 2024
Action Type Old Value New Value -
CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
May. 14, 2024
Action Type Old Value New Value -
Initial Analysis by [email protected]
Apr. 10, 2024
Action Type Old Value New Value Added CVSS V3.1 NIST AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N Changed Reference Type https://git.kernel.org/stable/c/5902f9453a313be8fe78cbd7e7ca9dba9319fc6e No Types Assigned https://git.kernel.org/stable/c/5902f9453a313be8fe78cbd7e7ca9dba9319fc6e Patch Changed Reference Type https://git.kernel.org/stable/c/82808cc026811fbc3ecf0c0b267a12a339eead56 No Types Assigned https://git.kernel.org/stable/c/82808cc026811fbc3ecf0c0b267a12a339eead56 Patch Changed Reference Type https://git.kernel.org/stable/c/82fa9ced35d88581cffa4a1c856fc41fca96d80a No Types Assigned https://git.kernel.org/stable/c/82fa9ced35d88581cffa4a1c856fc41fca96d80a Patch Changed Reference Type https://git.kernel.org/stable/c/84a24bf8c52e66b7ac89ada5e3cfbe72d65c1896 No Types Assigned https://git.kernel.org/stable/c/84a24bf8c52e66b7ac89ada5e3cfbe72d65c1896 Patch Changed Reference Type https://git.kernel.org/stable/c/d558fcdb17139728347bccc60a16af3e639649d2 No Types Assigned https://git.kernel.org/stable/c/d558fcdb17139728347bccc60a16af3e639649d2 Patch Added CWE NIST CWE-668 Added CPE Configuration OR *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 4.15.0 up to (excluding) 4.19.189 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 4.20.0 up to (excluding) 5.4.115 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.5.0 up to (excluding) 5.10.33 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.11.0 up to (excluding) 5.11.17 -
CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Feb. 27, 2024
Action Type Old Value New Value Added 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()] Added Reference Linux https://git.kernel.org/stable/c/5902f9453a313be8fe78cbd7e7ca9dba9319fc6e [No types assigned] Added Reference Linux https://git.kernel.org/stable/c/82808cc026811fbc3ecf0c0b267a12a339eead56 [No types assigned] Added Reference Linux https://git.kernel.org/stable/c/82fa9ced35d88581cffa4a1c856fc41fca96d80a [No types assigned] Added Reference Linux https://git.kernel.org/stable/c/d558fcdb17139728347bccc60a16af3e639649d2 [No types assigned] Added Reference Linux https://git.kernel.org/stable/c/84a24bf8c52e66b7ac89ada5e3cfbe72d65c1896 [No types assigned]
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2021-46921
is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2021-46921
weaknesses.