Linux Kernel up to 5.11.16 qrwlock queued_write_lock_slowpath comparison

Summaryinfo

A vulnerability was found in Linux Kernel up to 4.19.188/5.4.114/5.10.32/5.11/5.11.16 and classified as problematic. The impacted element is the function queued_write_lock_slowpath of the component qrwlock. Such manipulation leads to comparison. This vulnerability is listed as CVE-2021-46921. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 4.19.188/5.4.114/5.10.32/5.11/5.11.16 (Operating System). It has been rated as problematic. Affected by this issue is the function queued_write_lock_slowpath of the component qrwlock. The manipulation with an unknown input leads to a comparison vulnerability. Using CWE to declare the problem leads to CWE-697. The product compares two entities in a security-relevant context, but the comparison is incorrect, which may lead to resultant weaknesses. The impact remains unknown. CVE summarizes:

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()]

The weakness was presented 02/27/2024. The advisory is shared for download at git.kernel.org. This vulnerability is handled as CVE-2021-46921 since 02/25/2024. There are known technical details, but no exploit is available.

Upgrading to version 4.19.189, 5.4.115, 5.10.33, 5.11.17 or 5.12 eliminates this vulnerability. Applying the patch 5902f9453a31/82808cc02681/82fa9ced35d8/d558fcdb1713/84a24bf8c52e is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 4.19.188
• 5.0
• 5.1
• 5.2
• 5.3
• 5.4
• 5.4.114
• 5.5
• 5.6
• 5.7
• 5.8
• 5.9
• 5.10
• 5.10.0
• 5.10.1
• 5.10.2
• 5.10.3
• 5.10.4
• 5.10.5
• 5.10.6
• 5.10.7
• 5.10.8
• 5.10.9
• 5.10.10
• 5.10.11
• 5.10.12
• 5.10.13
• 5.10.14
• 5.10.15
• 5.10.16
• 5.10.17
• 5.10.18
• 5.10.19
• 5.10.20
• 5.10.21
• 5.10.22
• 5.10.23
• 5.10.24
• 5.10.25
• 5.10.26
• 5.10.27
• 5.10.28
• 5.10.29
• 5.10.30
• 5.10.31
• 5.10.32
• 5.11
• 5.11.0
• 5.11.1
• 5.11.2
• 5.11.3
• 5.11.4
• 5.11.5
• 5.11.6
• 5.11.7
• 5.11.8
• 5.11.9
• 5.11.10
• 5.11.11
• 5.11.12
• 5.11.13
• 5.11.14
• 5.11.15
• 5.11.16

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Entryinfo

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