CVE-2026-63883 serial: qcom_geni: fix kfifo underflow when flush precedes DMA completion IRQ
A race condition in the Qualcomm GENI serial driver allows stale buffer data exposure or denial of service when a flush occurs before DMA completion.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63883?
CVE-2026-63883 is a high-severity vulnerability in Linux, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-63883?
How do I fix CVE-2026-63883?
Apply the vendor's patch.
Is CVE-2026-63883 being exploited?
There is no known exploitation of CVE-2026-63883 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-63883, DEBIAN-CVE-2026-63883, GHSA-rjh6-3wfg-m2hh, UBUNTU-CVE-2026-63883.