Wind River Support Network

Description

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.