CVE-2026-63883

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> serial: qcom_geni: fix kfifo underflow when flush precedes DMA completion IRQ<br /> <br /> When uart_flush_buffer() runs before the DMA completion IRQ is delivered,<br /> the following race can occur (all steps serialized by uart_port_lock):<br /> <br /> 1. DMA starts: tx_remaining = N, kfifo contains N bytes<br /> 2. DMA completes in hardware; IRQ is pending but not yet delivered<br /> 3. uart_flush_buffer() acquires the port lock and calls kfifo_reset(),<br /> making kfifo_len() = 0 while tx_remaining remains N<br /> 4. uart_flush_buffer() releases the port lock<br /> 5. DMA IRQ fires; handle_tx_dma() acquires the port lock and calls<br /> uart_xmit_advance(uport, tx_remaining) on an empty kfifo<br /> <br /> uart_xmit_advance() increments kfifo-&gt;out by tx_remaining. Since<br /> kfifo_reset() already set both in and out to 0, out wraps past in,<br /> causing kfifo_len() to return UART_XMIT_SIZE - tx_remaining. The next<br /> start_tx_dma() call then submits a DMA transfer of stale buffer data.<br /> <br /> Fix this by snapshotting kfifo_len() at the start of handle_tx_dma()<br /> and skipping uart_xmit_advance() when fifo_len