Buffer Underflow Affecting kernel-zfcpdump package, versions *


Severity

Recommended
medium

Based on CentOS security rating.

Threat Intelligence

EPSS
0.16% (6th percentile)

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  • Snyk IDSNYK-CENTOS10-KERNELZFCPDUMP-18152829
  • published22 Jul 2026
  • disclosed19 Jul 2026

Introduced: 19 Jul 2026

NewCVE-2026-63883  (opens in a new tab)
CWE-124  (opens in a new tab)

How to fix?

There is no fixed version for Centos:10 kernel-zfcpdump.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-zfcpdump package and not the kernel-zfcpdump package as distributed by Centos. See How to fix? for Centos:10 relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1