{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-63883","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-07-19T07:54:57.018Z","datePublished":"2026-07-19T14:54:56.356Z","dateUpdated":"2026-08-05T12:36:52.126Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T12:36:52.126Z"},"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->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"}}}}