CVE-2026-68369 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
usb: gadget: printer: fix infinite loop in printer_read()
printer_read() uses the same variable for the requested copy size and the number of bytes actually copied to user space. copy_to_user() returns the number of bytes not copied, so when it fails to copy anything, the computed copied length becomes zero.
In that case len, buf, current_rx_bytes and current_rx_buf are left unchanged. If RX data is available and the user buffer remains unwritable, the read loop can repeat indefinitely.
Track the copied length separately and return -EFAULT, or the number of bytes already copied, if an iteration makes no progress.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability described represents a critical infinite loop condition within the Linux kernel's USB gadget printer driver implementation that could lead to system instability and denial of service. This flaw exists in the printer_read() function where improper handling of copy operation results creates a scenario where the function fails to advance its internal state variables during failed user space memory operations. The technical root cause stems from the misuse of a single variable to track both the requested data size for copying and the actual number of bytes successfully copied to user space, creating a logical error in the loop control mechanism.
The flaw manifests when copy_to_user() fails to transfer data to user space, returning zero as the count of bytes not copied. This return value incorrectly resets the tracking variable that should represent the actual bytes transferred, leaving all relevant state variables including len, buf, current_rx_bytes and current_rx_buf unchanged. When available RX data exists but the user buffer remains unwritable due to memory constraints or access violations, this condition causes the read loop to perpetually repeat without making progress. The function fails to properly detect when no forward progress is possible and therefore cannot break out of the loop to return appropriate error codes or partial data transfers.
This vulnerability directly maps to CWE-835, which addresses infinite loops in software systems, and aligns with ATT&CK technique T1499.004 for network denial of service attacks that can be leveraged through kernel-level vulnerabilities. The operational impact extends beyond simple system hang conditions as the infinite loop consumes CPU cycles continuously while maintaining no progress in data transfer operations, effectively creating a resource exhaustion scenario that can be exploited to disrupt legitimate system services and potentially cause system crashes or forced reboots. The vulnerability affects systems running Linux kernels with USB gadget printer functionality enabled, particularly those implementing printer device emulation capabilities.
Mitigation strategies must address both immediate defensive measures and long-term code structure improvements to prevent similar issues in the kernel's USB subsystem. Immediate fixes should involve modifying the printer_read() function to track the actual copied bytes separately from the requested copy size, ensuring that when copy_to_user() fails to transfer any data, the function properly detects this condition and either returns -EFAULT indicating a failure to copy data or returns the number of bytes successfully transferred in previous iterations. The implementation should also include timeout mechanisms or maximum iteration limits to prevent indefinite looping regardless of the underlying cause. System administrators should ensure kernel updates are applied promptly when patches are available, while developers should conduct thorough code reviews focusing on state variable management and loop control structures in kernel modules handling user space memory operations.