CVE-2026-63883 (GCVE-0-2026-63883)
Vulnerability from cvelistv5
Published
2026-07-19 14:54
Modified
2026-08-05 12:36
Severity ?
7.3 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L
Summary
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 2aaa43c7077833301c237684cd7bc9ae5e3dec95
Version: 2aaa43c7077833301c237684cd7bc9ae5e3dec95
Version: 2aaa43c7077833301c237684cd7bc9ae5e3dec95
Version: 2aaa43c7077833301c237684cd7bc9ae5e3dec95
Version: 2aaa43c7077833301c237684cd7bc9ae5e3dec95
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/tty/serial/qcom_geni_serial.c"
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          "product": "Linux",
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          ],
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          "vendor": "Linux",
          "versions": [
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              "version": "6.3"
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              "version": "0",
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              "status": "unaffected",
              "version": "6.12.93",
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            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.35",
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            {
              "lessThanOrEqual": "7.0.*",
              "status": "unaffected",
              "version": "7.0.12",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.143",
                  "versionStartIncluding": "6.3",
                  "vulnerable": true
                },
                {
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                  "versionEndExcluding": "6.12.93",
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              "negate": false,
              "operator": "OR"
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        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.3,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is reachable only through local TTY syscalls (open/write/ioctl/close) on Qualcomm GENI high-speed UART device nodes (e.g. /dev/ttyHS*); it is not triggered by remote network packets or physical bus manipulation alone.\nAC:L - An attacker who can open the port controls both sides of the race by writing to start DMA TX and immediately issuing TCFLSH/TCOFLUSH (or closing the port) to call uart_flush_buffer() before the DMA completion IRQ runs, and can repeat until the window is hit.\nPR:L - Exploitation requires only the ability to open and ioctl the UART TTY device (typically dialout-group membership or equivalent service access on Qualcomm Android/automotive/embedded platforms), not init-namespace root or capabilities obtainable only outside user namespaces.\nUI:N - Triggering the flush-vs-DMA-IRQ race requires no victim interaction beyond the attacker\u0027s own writes and flush/close operations on the serial port.\nS:U - Impact is confined to kernel serial-driver state and data transmitted on the local UART; it does not cross VM, container, or IOMMU security boundaries.\nC:H - The kfifo index underflow corrupts transmit FIFO bookkeeping and can cause a spurious large DMA read of stale xmit_buf contents (up to UART_XMIT_SIZE/PAGE_SIZE), leaking prior sensitive serial traffic (modem/BT/RS485 diagnostics) that should have been discarded by flush.\nI:H - The corrupted kfifo state causes unauthorized transmission of stale or attacker-influenced buffer data over the UART/RS485 line, corrupting the integrity of serial output to connected devices (ECUs, modems, factory controllers) beyond what the attacker legitimately queued.\nA:L - The primary impact is corrupted driver transmit state and spurious/erroneous serial output rather than a demonstrated kernel oops/panic; however, repeated triggering can degrade or disrupt serial communication relied on by connected subsystems."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:36:52.126Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/c91ea13375f70f6271a0183445e34e83b8f4d8f7"
        },
        {
          "url": "https://git.kernel.org/stable/c/b1159dce10b38eb795e4c96cdc4d34b83cec81c5"
        },
        {
          "url": "https://git.kernel.org/stable/c/654f45a8569f3cd6ff20bd724a18e0cce65893ba"
        },
        {
          "url": "https://git.kernel.org/stable/c/0d2c41a8b00934ddf8a7c1b4cf72dffa1e629c46"
        },
        {
          "url": "https://git.kernel.org/stable/c/452d6fa37ae9b021f4f6d397dbae077f7296f6f4"
        }
      ],
      "title": "serial: qcom_geni: fix kfifo underflow when flush precedes DMA completion IRQ",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63883",
    "datePublished": "2026-07-19T14:54:56.356Z",
    "dateReserved": "2026-07-19T07:54:57.018Z",
    "dateUpdated": "2026-08-05T12:36:52.126Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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