CVE-2026-63883 Details
Description
In the Linux kernel, the following vulnerability has been resolved: serial: qcom_geni: fix kfifo underflow when flush precedes DMA completion IRQ When uart_flush_buffer() runs before the DMA completion IRQ is delivered, the following race can occur (all steps serialized by uart_port_lock): 1. DMA starts: tx_remaining = N, kfifo contains N bytes 2. DMA completes in hardware; IRQ is pending but not yet delivered 3. uart_flush_buffer() acquires the port lock and calls kfifo_reset(), making kfifo_len() = 0 while tx_remaining remains N 4. uart_flush_buffer() releases the port lock 5. DMA IRQ fires; handle_tx_dma() acquires the port lock and calls uart_xmit_advance(uport, tx_remaining) on an empty kfifo uart_xmit_advance() increments kfifo->out by tx_remaining. Since kfifo_reset() already set both in and out to 0, out wraps past in, causing kfifo_len() to return UART_XMIT_SIZE - tx_remaining. The next start_tx_dma() call then submits a DMA transfer of stale buffer data. Fix this by snapshotting kfifo_len() at the start of handle_tx_dma() and skipping uart_xmit_advance() when fifo_len < tx_remaining, which indicates the kfifo was reset by a preceding flush.
A kfifo underflow vulnerability has been identified in the Linux kernel's Qcom GenI serial driver. This issue arises when the 'uart_flush_buffer()' function is called before the DMA completion interrupt is processed, creating a race condition. The problem occurs as follows: DMA transmission begins with 'tx_remaining' bytes, and the kfifo buffer holds the same number of bytes. Once the DMA completes in hardware, the interrupt is still pending. If 'uart_flush_buffer()' is executed at this point, it resets the kfifo length to zero while 'tx_remaining' remains unchanged. When the DMA interrupt finally arrives, it attempts to advance the transmission on an empty kfifo, leading to a situation where the kfifo length inaccurately reports available data. This miscalculation causes the next DMA transfer to include outdated buffer data, potentially disrupting the intended data transmission process.
Users can apply the latest patches available in the Linux kernel stable tree to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
No SSVC data is available for this CVE.
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Weakness Enumeration
No weakness enumeration is available for this CVE.
Affected Products
No affected product data is available for this CVE.
Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 20, 2026 | CVE Modified | kernel.org |
| Jul 19, 2026 | New CVE Received | kernel.org |