CVE-2026-89880 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
media: rtl2832_sdr: release URBs and stream buffers on start_streaming() failure
rtl2832_sdr_start_streaming() calls rtl2832_sdr_alloc_stream_bufs(), rtl2832_sdr_alloc_urbs() and rtl2832_sdr_submit_urbs() in sequence and shares a single err: label that only unlocks the mutex and returns. When alloc_urbs() succeeds but submit_urbs() fails, or when alloc_urbs() itself returns -ENOMEM after alloc_stream_bufs() has already succeeded, the URBs and/or the coherent DMA stream buffers stay allocated while streaming reports failure to vb2. Two latent defects follow on the next VIDIOC_STREAMON:
1) rtl2832_sdr_alloc_stream_bufs() unconditionally resets dev->buf_num to 0 and overwrites dev->buf_list[]/dev->dma_addr[], permanently
leaking the coherent DMA memory allocated by the previous attempt.
2) rtl2832_sdr_alloc_urbs() never resets dev->urbs_initialized and only increments it. After a second successful pass urbs_initialized can exceed MAX_BULK_BUFS, so the subsequent rtl2832_sdr_free_urbs() walks from urbs_initialized - 1 down to 0 and reads past the end of dev->urb_list[], passing garbage pointers to usb_free_urb().
Mirror the teardown that stop_streaming() already performs: on the error path call rtl2832_sdr_free_urbs() and rtl2832_sdr_free_stream_bufs() before unlocking. Both helpers are idempotent (free_urbs kills and zeros urbs_initialized; free_stream_bufs is gated on URB_BUF and clears the buf_num counter), so partial-failure paths and the no-allocation paths remain safe.
Issue identified by automated review of the INV-003 series at https://sashiko.dev/
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability in the Linux kernel media subsystem, specifically within the rtl2832_sdr driver, represents a critical resource management failure during the streaming initialization phase. The core technical flaw lies in the error handling logic of the rtl2832_sdr_start_streaming function. This routine sequentially allocates stream buffers and USB Request Blocks (URBs) before submitting them for data transfer. However, when an allocation or submission fails after partial success, the code jumps to a shared error label that merely unlocks a mutex and returns without releasing the previously allocated resources. This oversight results in coherent DMA memory and URB structures remaining allocated despite the streaming operation failing, creating a state of resource leakage that persists across subsequent driver invocations.
The operational impact of this flaw manifests through two distinct latent defects triggered by repeated attempts to start streaming via the VIDIOC_STREAMON ioctl. First, if stream buffer allocation succeeds but URB submission fails, or if URB allocation fails after buffers are allocated, the next attempt to start streaming causes rtl2832_sdr_alloc_stream_bufs to unconditionally reset the buffer counter and overwrite internal lists. This action permanently leaks the coherent DMA memory associated with the previous failed attempt because the driver does not free these resources before re-initializing them. Second, a more severe integrity issue arises from the handling of URB initialization counters. The function rtl2832_sdr_alloc_urbs increments a counter without resetting it on failure. Consequently, after multiple partial successes or failures, this counter can exceed its maximum limit, leading to an out-of-bounds memory access when the driver attempts to free URBs by iterating backwards from the inflated count. This results in reading garbage pointers and passing them to usb_free_urb, which poses a significant risk of kernel panic or arbitrary code execution due to invalid memory dereferences.
From a security taxonomy perspective, this vulnerability aligns with CWE-401, Missing Release of Memory after Effective Lifetime, as the driver fails to release allocated resources upon error conditions. Furthermore, the out-of-bounds read associated with the URB counter overflow relates directly to CWE-787, Out-of-bounds Read, which can lead to information disclosure or denial of service depending on how the kernel handles the invalid memory access. In terms of adversarial tactics, this flaw could be exploited in a Denial of Service attack by repeatedly triggering streaming failures to exhaust system resources through leaked DMA buffers and URB structures. Additionally, if an attacker can control the garbage pointers read during the overflow scenario, it may facilitate privilege escalation or remote code execution vectors within the kernel space, corresponding to ATT&CK techniques involving resource exhaustion and memory corruption exploitation.
To mitigate this vulnerability, the driver implementation must be updated to mirror the teardown logic present in the stop_streaming function. Specifically, on any error path following partial allocation of URBs or stream buffers, the code should explicitly call rtl2832_sdr_free_urbs and rtl2832_sdr_free_stream_bufs before unlocking the mutex and returning an error code. These helper functions are designed to be idempotent; free_urbs properly kills and zeros the urbs_initialized counter, preventing future overflow issues, while free_stream_bufs is gated on specific flags and clears buffer counters safely. This ensures that partial-failure paths do not leave dangling resources or corrupt state variables, thereby maintaining memory integrity and preventing both resource leaks and out-of-bounds accesses during subsequent streaming attempts.