GHSA-RJH6-3WFG-M2HH

Vulnerability from github – Published: 2026-07-19 18:31 – Updated: 2026-07-20 15:31
VLAI
Details

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.

Severity
7.3 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L
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{
  "affected": [],
  "aliases": [
    "CVE-2026-63883"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-19T16:17:05Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nserial: qcom_geni: fix kfifo underflow when flush precedes DMA completion IRQ\n\nWhen uart_flush_buffer() runs before the DMA completion IRQ is delivered,\nthe following race can occur (all steps serialized by uart_port_lock):\n\n  1. DMA starts: tx_remaining = N, kfifo contains N bytes\n  2. DMA completes in hardware; IRQ is pending but not yet delivered\n  3. uart_flush_buffer() acquires the port lock and calls kfifo_reset(),\n     making kfifo_len() = 0 while tx_remaining remains N\n  4. uart_flush_buffer() releases the port lock\n  5. DMA IRQ fires; handle_tx_dma() acquires the port lock and calls\n     uart_xmit_advance(uport, tx_remaining) on an empty kfifo\n\nuart_xmit_advance() increments kfifo-\u003eout by tx_remaining. Since\nkfifo_reset() already set both in and out to 0, out wraps past in,\ncausing kfifo_len() to return UART_XMIT_SIZE - tx_remaining. The next\nstart_tx_dma() call then submits a DMA transfer of stale buffer data.\n\nFix this by snapshotting kfifo_len() at the start of handle_tx_dma()\nand skipping uart_xmit_advance() when fifo_len \u003c tx_remaining, which\nindicates the kfifo was reset by a preceding flush.",
  "id": "GHSA-rjh6-3wfg-m2hh",
  "modified": "2026-07-20T15:31:49Z",
  "published": "2026-07-19T18:31:43Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63883"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0d2c41a8b00934ddf8a7c1b4cf72dffa1e629c46"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/452d6fa37ae9b021f4f6d397dbae077f7296f6f4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/654f45a8569f3cd6ff20bd724a18e0cce65893ba"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b1159dce10b38eb795e4c96cdc4d34b83cec81c5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c91ea13375f70f6271a0183445e34e83b8f4d8f7"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L",
      "type": "CVSS_V3"
    }
  ]
}



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