CVE-2026-64277 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
Input: synaptics-rmi4 - bound the F3A keymap to the GPIO count
rmi_f3a_initialize() takes the GPIO count from the device query register (f3a->gpio_count = buf & RMI_F3A_GPIO_COUNT, range 0..127). rmi_f3a_map_gpios() then allocates gpio_key_map with min(gpio_count, TRACKSTICK_RANGE_END) == at most 6 entries, but rmi_f3a_attention() iterates the full gpio_count and dereferences gpio_key_map[i], and input->keycodemax is set to the full gpio_count
while input->keycode points at the 6-entry allocation.
A device that reports gpio_count > 6 therefore causes an out-of-bounds read of gpio_key_map[] on every attention interrupt, and out-of-bounds
accesses through the input core's default keymap ioctls: EVIOCGKEYCODE reads past the buffer (leaking adjacent slab memory to user space) and EVIOCSKEYCODE writes a caller-controlled value past it, for any process able to open the evdev node, since input_default_getkeycode() and input_default_setkeycode() only bound the index against keycodemax.
Size the keymap for the full gpio_count. The mapping loop is unchanged: it still assigns only the first min(gpio_count, TRACKSTICK_RANGE_END) entries; the remaining slots stay KEY_RESERVED (devm_kcalloc zero-fills) and are skipped when reporting.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability exists within the linux kernel's synaptics-rmi4 driver where a memory corruption issue arises from improper handling of gpio keymap allocation and management. The flaw occurs during the initialization phase when rmi_f3a_initialize() reads the GPIO count from the device query register and stores it in f3a->gpio_count. This value can range from 0 to 127 as indicated by the bitwise operation with RMI_F3A_GPIO_COUNT mask. However, the subsequent rmi_f3a_map_gpios() function creates a gpio_key_map allocation that caps at TRACKSTICK_RANGE_END entries, which is at most 6 entries, despite the actual GPIO count potentially being higher.
The operational impact becomes critical during interrupt processing where rmi_f3a_attention() iterates through the full gpio_count value rather than the limited allocation size. This mismatch creates a fundamental out-of-bounds memory access pattern that affects both read and write operations. When the device reports a gpio_count greater than 6, every attention interrupt triggers an out-of-bounds read of the gpio_key_map array since the code dereferences gpio_key_map[i] for all i in range 0 to gpio_count-1 without proper bounds checking.
The vulnerability extends beyond simple memory corruption to include information leakage and potential privilege escalation scenarios. When input_default_getkeycode() processes EVIOCGKEYCODE ioctls, it reads past the allocated buffer boundary, causing adjacent slab memory to be leaked to user space processes that can open the evdev node. Similarly, input_default_setkeycode() with EVIOCSKEYCODE ioctls allows a caller-controlled value to be written past the end of the allocated buffer, creating potential for arbitrary memory corruption. This behavior stems from the input core's default keymap handling which only validates index bounds against keycodemax rather than against the actual allocation size.
This vulnerability aligns with CWE-129 Input Validation and CWE-787 Out-of-bounds Write categories, demonstrating a classic buffer overflow pattern where array access exceeds allocated memory boundaries. The ATT&CK framework would classify this under T1068 Valid Accounts for privilege escalation potential, as any process with access to the evdev node could exploit this vulnerability. The issue represents a failure in bounds checking and memory management during device initialization, specifically in how the driver handles variable-length GPIO configurations from hardware devices.
The fix implements proper memory sizing by allocating the keymap buffer to accommodate the full gpio_count rather than limiting it to the TRACKSTICK_RANGE_END maximum. This ensures that all entries up to the actual GPIO count are properly allocated and accessible through the input core's default keymap ioctls. The mapping loop logic remains unchanged, still assigning only the first min(gpio_count, TRACKSTICK_RANGE_END) entries while leaving remaining slots as KEY_RESERVED due to the zero-filling behavior of devm_kcalloc. This approach maintains backward compatibility for devices with fewer GPIOs while preventing out-of-bounds access for devices reporting higher GPIO counts. The solution addresses the root cause by ensuring proper allocation sizing that matches the actual hardware capabilities reported by the device query register, thereby eliminating both the read and write vulnerabilities associated with improper memory bounds handling.