CVE-2026-63883

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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->out 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 < tx_remaining, which\nindicates the kfifo was reset by a preceding flush."}], "metrics": [{"cvssV3_1": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L", "baseScore": 7.3, "baseSeverity": "HIGH"}, "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's 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."}]}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["drivers/tty/serial/qcom_geni_serial.c"], "versions": [{"version": "2aaa43c7077833301c237684cd7bc9ae5e3dec95", "lessThan": "c91ea13375f70f6271a0183445e34e83b8f4d8f7", "status": "affected", "versionType": "git"}, {"version": "2aaa43c7077833301c237684cd7bc9ae5e3dec95", "lessThan": "b1159dce10b38eb795e4c96cdc4d34b83cec81c5", "status": "affected", "versionType": "git"}, {"version": "2aaa43c7077833301c237684cd7bc9ae5e3dec95", "lessThan": "654f45a8569f3cd6ff20bd724a18e0cce65893ba", "status": "affected", "versionType": "git"}, {"version": "2aaa43c7077833301c237684cd7bc9ae5e3dec95", "lessThan": "0d2c41a8b00934ddf8a7c1b4cf72dffa1e629c46", "status": "affected", "versionType": "git"}, {"version": "2aaa43c7077833301c237684cd7bc9ae5e3dec95", "lessThan": "452d6fa37ae9b021f4f6d397dbae077f7296f6f4", "status": "affected", "versionType": "git"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["drivers/tty/serial/qcom_geni_serial.c"], "versions": [{"version": "6.3", "status": "affected"}, {"version": "0", "lessThan": "6.3", "status": "unaffected", "versionType": "semver"}, {"version": "6.6.143", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.12.93", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.18.35", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.0.12", "lessThanOrEqual": "7.0.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.1", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3", "versionEndExcluding": "6.6.143"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3", "versionEndExcluding": "6.12.93"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3", "versionEndExcluding": "6.18.35"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3", "versionEndExcluding": "7.0.12"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3", "versionEndExcluding": "7.1"}]}]}], "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"}}}}

{}

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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->out 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 < tx_remaining, which\nindicates the kfifo was reset by a preceding flush."}], "id": "CVE-2026-63883", "lastModified": "2026-11-12T20:00:16.807", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "LOW", "baseScore": 7.3, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 5.5, "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary"}]}, "published": "2026-07-19T16:17:05.343", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/0d2c41a8b00934ddf8a7c1b4cf72dffa1e629c46"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/452d6fa37ae9b021f4f6d397dbae077f7296f6f4"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/654f45a8569f3cd6ff20bd724a18e0cce65893ba"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/b1159dce10b38eb795e4c96cdc4d34b83cec81c5"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/c91ea13375f70f6271a0183445e34e83b8f4d8f7"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-362"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: serial: qcom_geni: fix kfifo underflow when flush precedes DMA completion IRQ", "id": "2502364", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2502364"}, "csaw": false, "cvss3": {"cvss3_base_score": "7.0", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H", "status": "draft"}, "cwe": "CWE-124", "details": ["In the Linux kernel, the following vulnerability has been resolved:\nserial: qcom_geni: fix kfifo underflow when flush precedes DMA completion IRQ\nWhen uart_flush_buffer() runs before the DMA completion IRQ is delivered,\nthe following race can occur (all steps serialized by uart_port_lock):\n1. DMA starts: tx_remaining = N, kfifo contains N bytes\n2. DMA completes in hardware; IRQ is pending but not yet delivered\n3. uart_flush_buffer() acquires the port lock and calls kfifo_reset(),\nmaking kfifo_len() = 0 while tx_remaining remains N\n4. uart_flush_buffer() releases the port lock\n5. DMA IRQ fires; handle_tx_dma() acquires the port lock and calls\nuart_xmit_advance(uport, tx_remaining) on an empty kfifo\nuart_xmit_advance() increments kfifo->out 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.\nFix this by snapshotting kfifo_len() at the start of handle_tx_dma()\nand skipping uart_xmit_advance() when fifo_len < tx_remaining, which\nindicates the kfifo was reset by a preceding flush.", "A flaw was found in the Linux kernel's qcom_geni serial driver. A race condition can occur when the uart_flush_buffer() function executes before the Direct Memory Access (DMA) completion interrupt is processed. This timing issue can lead to a kernel First-In, First-Out (kfifo) buffer underflow. Consequently, stale buffer data may be transferred via DMA, potentially leading to information disclosure or data integrity issues."], "name": "CVE-2026-63883", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Fix deferred", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2026-07-19T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-63883\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-63883\nhttps://lore.kernel.org/linux-cve-announce/2026071939-CVE-2026-63883-bdaa@gregkh/T"], "threat_severity": "Moderate"}

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