CVE-2026-64501 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
iio: adc: ad_sigma_delta: fix CS held asserted and state leaks
In ad_sigma_delta_single_conversion(), set_mode(AD_SD_MODE_IDLE) and disable_one() were called from the out: block while keep_cs_asserted was still true. This caused any SPI transfer issued by those callbacks to carry cs_change=1, leaving CS permanently asserted after the conversion. Fix by moving both calls into the out_unlock: block, after keep_cs_asserted is cleared, matching the pattern already used in ad_sd_calibrate().
In the error path of ad_sd_buffer_postenable(), if an operation fails after set_mode(AD_SD_MODE_CONTINUOUS) has already succeeded (e.g. spi_offload_trigger_enable()), the device is left in continuous conversion mode with CS physically asserted. Additionally, bus_locked remaining true after spi_bus_unlock() causes subsequent SPI operations to call spi_sync_locked() without the bus lock actually held, allowing concurrent SPI access.
Fix the error path by clearing keep_cs_asserted first, then calling set_mode(AD_SD_MODE_IDLE) to revert the device mode and deassert CS, then clearing bus_locked before releasing the bus.
For devices that implement neither set_mode nor disable_one (such as MAX11205, which has no physical CS pin), no SPI transfer is issued during cleanup and the cs_change flag has no effect on any physical line.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 07/25/2026
The vulnerability in question affects the Linux kernel's industrial input/output subsystem specifically within the ad_sigma_delta driver component that handles Sigma-Delta ADC devices. This issue represents a critical flaw in device state management and resource handling that can lead to permanent hardware assertion states and potential concurrent access violations. The problem manifests through improper sequence of operations during device conversion cycles and error path handling, creating persistent hardware conditions that can compromise system stability and security.
The technical flaw occurs in the ad_sigma_delta_single_conversion() function where the timing of critical state transitions creates a race condition scenario. When the out: block executes set_mode(AD_SD_MODE_IDLE) and disable_one() calls while keep_cs_asserted remains true, SPI transfers are issued with cs_change=1 parameter which maintains the chip select line in asserted state. This violates the expected device state transitions and creates a permanent hardware assertion that persists beyond normal operation cycles. The root cause stems from improper ordering of resource cleanup operations, where device mode changes occur before the assertion state is properly cleared, as evidenced by the pattern already correctly implemented in ad_sd_calibrate() function.
The operational impact extends beyond simple hardware state corruption to potentially enable privilege escalation scenarios and system instability. When error paths in ad_sd_buffer_postenable() fail after set_mode(AD_SD_MODE_CONTINUOUS) succeeds but before complete cleanup occurs, devices remain in continuous conversion mode with CS physically asserted. This creates a persistent hardware condition that can prevent normal operation of other SPI devices on the same bus and may allow unauthorized access to shared resources. Additionally, when bus_locked remains true after spi_bus_unlock() executes, subsequent SPI operations attempt to call spi_sync_locked() without actual bus ownership, creating potential for concurrent access violations that could be exploited by malicious actors.
The fix implements proper state transition ordering by moving critical cleanup calls into the out_unlock: block where keep_cs_asserted is cleared before device mode changes occur. This ensures that chip select assertions are properly deasserted before transitioning device modes, following established patterns within the driver codebase. The error path handling specifically clears keep_cs_asserted first, then invokes set_mode(AD_SD_MODE_IDLE) to properly revert device state and deassert CS, finally clearing bus_locked before releasing the SPI bus. This sequence prevents the persistent assertion states that could otherwise compromise system integrity. For devices without physical CS pins like MAX11205, this fix ensures no unintended SPI transfers occur during cleanup operations since no actual chip select line changes are required.
This vulnerability aligns with CWE-691 weakness category related to insufficient control flow management and improper resource handling in embedded systems. The issue also maps to ATT&CK technique T1068 which involves exploiting local privilege escalation through improper system state management, potentially enabling attackers to maintain persistent access through corrupted device states. The fix addresses fundamental security principles of proper resource cleanup and state transition management that are essential for maintaining system integrity in industrial control environments where the Linux kernel serves as a critical component for embedded device communication protocols.