Exposure of Resource to Wrong Sphere Affecting kernel-64kb package, versions <5.3.18-150300.59.158.1
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-SLES153-KERNEL64KB-7720574
- published20 Aug 2024
- disclosed3 May 2024
Introduced: 3 May 2024
CVE-2021-46921 (opens in a new tab)How to fix?
Upgrade SLES:15.3 kernel-64kb to version 5.3.18-150300.59.158.1 or higher.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-64kb package and not the kernel-64kb package as distributed by SLES.
See How to fix? for SLES:15.3 relevant fixed versions and status.
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()]
References
- https://www.suse.com/security/cve/CVE-2021-46921.html
- https://bugzilla.suse.com/1220468
- https://git.kernel.org/stable/c/5902f9453a313be8fe78cbd7e7ca9dba9319fc6e
- https://git.kernel.org/stable/c/82808cc026811fbc3ecf0c0b267a12a339eead56
- https://git.kernel.org/stable/c/82fa9ced35d88581cffa4a1c856fc41fca96d80a
- https://git.kernel.org/stable/c/84a24bf8c52e66b7ac89ada5e3cfbe72d65c1896
- https://git.kernel.org/stable/c/d558fcdb17139728347bccc60a16af3e639649d2