Linux Kernel up to 7.2.5 xilinx_dma xilinx_dma_poll_timeout delay_us race condition

Summaryinfo

A vulnerability described as critical has been identified in Linux Kernel up to 7.2.5. The affected element is the function xilinx_dma_poll_timeout of the component xilinx_dma. The manipulation of the argument delay_us results in race condition. This vulnerability is known as CVE-2026-93168. It is possible to launch the attack remotely. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as critical has been found in Linux Kernel up to 7.2.5. Affected is the function xilinx_dma_poll_timeout of the component xilinx_dma. The manipulation of the argument delay_us with an unknown input leads to a race condition vulnerability. CWE is classifying the issue as CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. This is going to have an impact on availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: dmaengine: xilinx_dma: Fix CPU stall in xilinx_dma_poll_timeout Currently when calling xilinx_dma_poll_timeout with delay_us=0 and a condition that is never fulfilled, the CPU busy-waits for prolonged time and the timeout triggers only with a massive delay causing a CPU stall. This happens due to a huge underestimation of wall clock time in poll_timeout_us_atomic. Commit 7349a69cf312 ("iopoll: Do not use timekeeping in read_poll_timeout_atomic()") changed the behavior to no longer use ktime_get at the expense of underestimation of wall clock time which appears to be very large for delay_us=0. Instead of timing out after approximately XILINX_DMA_LOOP_COUNT microseconds, the timeout takes XILINX_DMA_LOOP_COUNT * 1000 * (time that the overhead of the for loop in poll_timeout_us_atomic takes) which is in the range of several minutes for XILINX_DMA_LOOP_COUNT=1000000. Fix this by using a non-zero value for delay_us. Use delay_us=10 to keep the delay in the hot path of starting DMA transfers minimal but still avoid CPU stalls in case of unexpected hardware failures. One-off measurement with delay_us=0 causes the cpu to busy wait around 7 minutes in the timeout case. After applying this patch with delay_us=10 the measured timeout was 1053428 microseconds which is roughly equivalent to the expected 1000000 microseconds specified in XILINX_DMA_LOOP_COUNT. Add a constant XILINX_DMA_POLL_DELAY_US for delay_us value.

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2026-93168 since 09/17/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/17/2026).

Upgrading to version 7.2.6 or 7.3-rc1 eliminates this vulnerability. Applying the patch 8b5654d317277e6e505c23f8fa7e415237fefc7f/aa99c4d1d63bbc26a5fc4c667d89b2595743c19d is able to eliminate this problem. 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

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5

License

• open-source

Website

• Vendor: https://www.kernel.org/

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