iio: adc: ad_sigma_delta: fix use-after-free on unbind

Overview

In the Linux kernel, the following vulnerability has been resolved:

iio: adc: ad_sigma_delta: fix use-after-free on unbind

ad_sd_buffer_postenable() allocates sigma_delta->samples_buf with devm_krealloc() at runtime, so its devres entry sits after all probe-time entries of the driver. devm resources are released in reverse allocation order, which means unbind frees samples_buf before iio_device_unregister() disables the buffers and detaches the trigger pollfunc. The data ready IRQ is still enabled at that point, so ad_sd_trigger_handler() can still run and memcpy() incoming samples into the freed samples_buf.

Fix this by preallocating the buffer in devm_ad_sd_setup_buffer_and_trigger(), before the triggered buffer and the IRQ are set up, so it is freed only after iio_device_unregister() has drained the trigger handler via free_irq(). Size it for the worst case of all sequencer slots being active; ad_sd_validate_scan_mask() already caps the number of active channels at num_slots.

This issue was found by an in-house static analysis tool.

Affected

• Linux >= 8bea9af887de4c99a95f93f2ce400ef63e8b4e9b < 84500ae0d976995a6870cb1dca2d124b6b2d6e5a
• Linux >= 8bea9af887de4c99a95f93f2ce400ef63e8b4e9b < f20b94a7dc1ff9ade191ce839c984210fdbdc653
• Linux >= 8bea9af887de4c99a95f93f2ce400ef63e8b4e9b < 5663c72bf400231e90777982216797191887a6b9
• Linux >= 8bea9af887de4c99a95f93f2ce400ef63e8b4e9b < 9ee8306121495d2a25aa5d1bfd519f2748786b83
• Linux 5.19

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.