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 version of kernel installed on the remote host is prior to 5.10.29-27.128. It is, therefore, affected by a vulnerability as referenced in the ALAS2KERNEL-5.10-2024-055 advisory.

  - 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()]     (CVE-2021-46921)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The version of kernel installed on the remote host is prior to 5.4.110-54.189. It is, therefore, affected by a vulnerability as referenced in the ALAS2KERNEL-5.4-2024-063 advisory.

  - 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()]     (CVE-2021-46921)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

ID	Name	Product	Family	Severity
195662	RHEL 6 : kernel (Unpatched Vulnerability)	Nessus	Red Hat Local Security Checks	critical
195652	RHEL 7 : kernel (Unpatched Vulnerability)	Nessus	Red Hat Local Security Checks	critical
194864	Amazon Linux 2 : kernel (ALASKERNEL-5.10-2024-055)	Nessus	Amazon Linux Local Security Checks	medium
194854	Amazon Linux 2 : kernel (ALASKERNEL-5.4-2024-063)	Nessus	Amazon Linux Local Security Checks	medium
194454	SUSE SLES15 Security Update : kernel (SUSE-SU-2024:1454-1)	Nessus	SuSE Local Security Checks	high
192503	SUSE SLES12 Security Update : kernel (SUSE-SU-2024:0975-1)	Nessus	SuSE Local Security Checks	high
192501	SUSE SLES12 Security Update : kernel (SUSE-SU-2024:0976-1)	Nessus	SuSE Local Security Checks	high
192499	SUSE SLED12 / SLES12 Security Update : kernel (SUSE-SU-2024:0925-1)	Nessus	SuSE Local Security Checks	high

Detections

Analytics

CVE-2021-46921

medium

Tenable Plugins

critical

critical

medium

medium

high

high

high

high