Bug 2466777 (CVE-2026-43061)

Summary: CVE-2026-43061 kernel: serial: 8250: Fix TX deadlock when using DMA
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's 8250 serial driver when utilizing Direct Memory Access (DMA). An issue arises when a DMA transaction is terminated asynchronously, as the system may not properly clear the `dma->tx_running` flag. This prevents subsequent transmit (TX) DMA transactions from being scheduled, leading to a deadlock. This vulnerability can result in a Denial of Service (DoS), rendering the serial communication unresponsive.
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Description OSIDB Bzimport 2026-05-05 17:02:04 UTC 
In the Linux kernel, the following vulnerability has been resolved:

serial: 8250: Fix TX deadlock when using DMA

`dmaengine_terminate_async` does not guarantee that the
`__dma_tx_complete` callback will run. The callback is currently the
only place where `dma->tx_running` gets cleared. If the transaction is
canceled and the callback never runs, then `dma->tx_running` will never
get cleared and we will never schedule new TX DMA transactions again.

This change makes it so we clear `dma->tx_running` after we terminate
the DMA transaction. This is "safe" because `serial8250_tx_dma_flush`
is holding the UART port lock. The first thing the callback does is also
grab the UART port lock, so access to `dma->tx_running` is serialized.
Comment 1 Alexander B 2026-05-06 09:55:35 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050537-CVE-2026-43061-91b7@gregkh/T